Merge Chromium at r65505: Initial merge by git.

Change-Id: I31d8f1d8cd33caaf7f47ffa7350aef42d5fbdb45

32 files changed, 2734 insertions, 1993 deletions

diff --git a/chrome/browser/history/archived_database.cc b/chrome/browser/history/archived_database.cc
index 72fa998..08a742f 100644
--- a/chrome/browser/history/archived_database.cc
+++ b/chrome/browser/history/archived_database.cc
@@ -62,6 +62,7 @@ bool ArchivedDatabase::Init(const FilePath& file_name) {
     return false;
   }
   CreateMainURLIndex();
+  CreateKeywordSearchTermsIndices();
 
   if (EnsureCurrentVersion() != sql::INIT_OK) {
     db_.Close();
diff --git a/chrome/browser/history/expire_history_backend_unittest.cc b/chrome/browser/history/expire_history_backend_unittest.cc
index 91129ed..3177dde 100644
--- a/chrome/browser/history/expire_history_backend_unittest.cc
+++ b/chrome/browser/history/expire_history_backend_unittest.cc
@@ -8,6 +8,7 @@
 #include "base/file_util.h"
 #include "base/path_service.h"
 #include "base/scoped_ptr.h"
+#include "base/scoped_temp_dir.h"
 #include "base/string16.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/bookmarks/bookmark_model.h"
@@ -31,7 +32,6 @@ using base::TimeDelta;
 using base::TimeTicks;
 
 // Filename constants.
-static const FilePath::CharType kTestDir[] = FILE_PATH_LITERAL("ExpireTest");
 static const FilePath::CharType kHistoryFile[] = FILE_PATH_LITERAL("History");
 static const FilePath::CharType kArchivedHistoryFile[] =
     FILE_PATH_LITERAL("Archived History");
@@ -49,6 +49,8 @@ class ExpireHistoryTest : public testing::Test,
  public:
   ExpireHistoryTest()
       : bookmark_model_(NULL),
+        ui_thread_(BrowserThread::UI, &message_loop_),
+        db_thread_(BrowserThread::DB, &message_loop_),
         ALLOW_THIS_IN_INITIALIZER_LIST(expirer_(this, &bookmark_model_)),
         now_(Time::Now()) {
   }
@@ -85,9 +87,17 @@ class ExpireHistoryTest : public testing::Test,
 
   static bool IsStringInFile(const FilePath& filename, const char* str);
 
+  // Returns the path the db files are created in.
+  const FilePath& path() const { return tmp_dir_.path(); }
+
+  // This must be destroyed last.
+  ScopedTempDir tmp_dir_;
+
   BookmarkModel bookmark_model_;
 
-  MessageLoop message_loop_;
+  MessageLoopForUI message_loop_;
+  BrowserThread ui_thread_;
+  BrowserThread db_thread_;
 
   ExpireHistoryBackend expirer_;
 
@@ -108,43 +118,40 @@ class ExpireHistoryTest : public testing::Test,
       NotificationList;
   NotificationList notifications_;
 
-  // Directory for the history files.
-  FilePath dir_;
-
  private:
   void SetUp() {
-    FilePath temp_dir;
-    PathService::Get(base::DIR_TEMP, &temp_dir);
-    dir_ = temp_dir.Append(kTestDir);
-    file_util::Delete(dir_, true);
-    file_util::CreateDirectory(dir_);
+    ASSERT_TRUE(tmp_dir_.CreateUniqueTempDir());
 
-    FilePath history_name = dir_.Append(kHistoryFile);
+    FilePath history_name = path().Append(kHistoryFile);
     main_db_.reset(new HistoryDatabase);
     if (main_db_->Init(history_name, FilePath()) != sql::INIT_OK)
       main_db_.reset();
 
-    FilePath archived_name = dir_.Append(kArchivedHistoryFile);
+    FilePath archived_name = path().Append(kArchivedHistoryFile);
     archived_db_.reset(new ArchivedDatabase);
     if (!archived_db_->Init(archived_name))
       archived_db_.reset();
 
-    FilePath thumb_name = dir_.Append(kThumbnailFile);
+    FilePath thumb_name = path().Append(kThumbnailFile);
     thumb_db_.reset(new ThumbnailDatabase);
     if (thumb_db_->Init(thumb_name, NULL) != sql::INIT_OK)
       thumb_db_.reset();
 
-    text_db_.reset(new TextDatabaseManager(dir_,
+    text_db_.reset(new TextDatabaseManager(path(),
                                            main_db_.get(), main_db_.get()));
     if (!text_db_->Init(NULL))
       text_db_.reset();
 
     expirer_.SetDatabases(main_db_.get(), archived_db_.get(), thumb_db_.get(),
                           text_db_.get());
+    profile_.CreateTopSites();
+    profile_.BlockUntilTopSitesLoaded();
     top_sites_ = profile_.GetTopSites();
   }
 
   void TearDown() {
+    top_sites_ = NULL;
+
     ClearLastNotifications();
 
     expirer_.SetDatabases(NULL, NULL, NULL, NULL);
@@ -153,8 +160,6 @@ class ExpireHistoryTest : public testing::Test,
     archived_db_.reset();
     thumb_db_.reset();
     text_db_.reset();
-    TopSites::DeleteTopSites(top_sites_);
-    file_util::Delete(dir_, true);
   }
 
   // BroadcastNotificationDelegate implementation.
@@ -309,11 +314,13 @@ bool ExpireHistoryTest::HasFavIcon(FavIconID favicon_id) {
 }
 
 bool ExpireHistoryTest::HasThumbnail(URLID url_id) {
+  // TODO(sky): fix this. This test isn't really valid for TopSites. For
+  // TopSites we should be checking URL always, not the id.
   URLRow info;
   if (!main_db_->GetURLRow(url_id, &info))
     return false;
   GURL url = info.url();
-  RefCountedBytes *data;
+  scoped_refptr<RefCountedBytes> data;
   return top_sites_->GetPageThumbnail(url, &data);
 }
 
@@ -350,7 +357,8 @@ void ExpireHistoryTest::EnsureURLInfoGone(const URLRow& row) {
   EXPECT_EQ(0U, visits.size());
 
   // Thumbnail should be gone.
-  EXPECT_FALSE(HasThumbnail(row.id()));
+  // TODO(sky): fix this, see comment in HasThumbnail.
+  // EXPECT_FALSE(HasThumbnail(row.id()));
 
   // Check the notifications. There should be a delete notification with this
   // URL in it. There should also be a "typed URL changed" notification if the
@@ -439,7 +447,8 @@ TEST_F(ExpireHistoryTest, FLAKY_DeleteURLAndFavicon) {
   URLRow last_row;
   ASSERT_TRUE(main_db_->GetURLRow(url_ids[2], &last_row));
   EXPECT_TRUE(HasFavIcon(last_row.favicon_id()));
-  EXPECT_TRUE(HasThumbnail(url_ids[2]));
+  // TODO(sky): fix this, see comment in HasThumbnail.
+  // EXPECT_TRUE(HasThumbnail(url_ids[2]));
 
   VisitVector visits;
   main_db_->GetVisitsForURL(url_ids[2], &visits);
@@ -452,14 +461,14 @@ TEST_F(ExpireHistoryTest, FLAKY_DeleteURLAndFavicon) {
                        visits[0].visit_time);
 
   // Compute the text DB filename.
-  FilePath fts_filename = dir_.Append(
+  FilePath fts_filename = path().Append(
       TextDatabase::IDToFileName(text_db_->TimeToID(visit_times[3])));
 
   // When checking the file, the database must be closed. We then re-initialize
   // it just like the test set-up did.
   text_db_.reset();
   EXPECT_TRUE(IsStringInFile(fts_filename, "goats"));
-  text_db_.reset(new TextDatabaseManager(dir_,
+  text_db_.reset(new TextDatabaseManager(path(),
                                          main_db_.get(), main_db_.get()));
   ASSERT_TRUE(text_db_->Init(NULL));
   expirer_.SetDatabases(main_db_.get(), archived_db_.get(), thumb_db_.get(),
@@ -472,7 +481,7 @@ TEST_F(ExpireHistoryTest, FLAKY_DeleteURLAndFavicon) {
   // doesn't remove it from the file, we want to be sure we're doing the latter.
   text_db_.reset();
   EXPECT_FALSE(IsStringInFile(fts_filename, "goats"));
-  text_db_.reset(new TextDatabaseManager(dir_,
+  text_db_.reset(new TextDatabaseManager(path(),
                                          main_db_.get(), main_db_.get()));
   ASSERT_TRUE(text_db_->Init(NULL));
   expirer_.SetDatabases(main_db_.get(), archived_db_.get(), thumb_db_.get(),
@@ -500,7 +509,8 @@ TEST_F(ExpireHistoryTest, DeleteURLWithoutFavicon) {
   URLRow last_row;
   ASSERT_TRUE(main_db_->GetURLRow(url_ids[1], &last_row));
   EXPECT_TRUE(HasFavIcon(last_row.favicon_id()));
-  EXPECT_TRUE(HasThumbnail(url_ids[1]));
+  // TODO(sky): fix this, see comment in HasThumbnail.
+  // EXPECT_TRUE(HasThumbnail(url_ids[1]));
 
   VisitVector visits;
   main_db_->GetVisitsForURL(url_ids[1], &visits);
@@ -546,7 +556,8 @@ TEST_F(ExpireHistoryTest, DontDeleteStarredURL) {
   ASSERT_EQ(0U, visits.size());
 
   // Should still have the thumbnail.
-  ASSERT_TRUE(HasThumbnail(url_row.id()));
+  // TODO(sky): fix this, see comment in HasThumbnail.
+  // ASSERT_TRUE(HasThumbnail(url_row.id()));
 
   // Unstar the URL and delete again.
   bookmark_model_.SetURLStarred(url, string16(), false);
@@ -604,7 +615,8 @@ TEST_F(ExpireHistoryTest, FlushRecentURLsUnstarred) {
 
   // Verify that the middle URL's favicon and thumbnail is still there.
   EXPECT_TRUE(HasFavIcon(url_row1.favicon_id()));
-  EXPECT_TRUE(HasThumbnail(url_row1.id()));
+  // TODO(sky): fix this, see comment in HasThumbnail.
+  // EXPECT_TRUE(HasThumbnail(url_row1.id()));
 
   // Verify that the last URL was deleted.
   EnsureURLInfoGone(url_row2);
@@ -660,12 +672,14 @@ TEST_F(ExpireHistoryTest, FlushRecentURLsUnstarredRestricted) {
 
   // Verify that the middle URL's favicon and thumbnail is still there.
   EXPECT_TRUE(HasFavIcon(url_row1.favicon_id()));
-  EXPECT_TRUE(HasThumbnail(url_row1.id()));
+  // TODO(sky): fix this, see comment in HasThumbnail.
+  // EXPECT_TRUE(HasThumbnail(url_row1.id()));
 
   // Verify that the last URL was not touched.
   EXPECT_TRUE(main_db_->GetURLRow(url_ids[2], &temp_row));
   EXPECT_TRUE(HasFavIcon(url_row2.favicon_id()));
-  EXPECT_TRUE(HasThumbnail(url_row2.id()));
+  // TODO(sky): fix this, see comment in HasThumbnail.
+  // EXPECT_TRUE(HasThumbnail(url_row2.id()));
 }
 
 // Expire a starred URL, it shouldn't get deleted
@@ -706,9 +720,11 @@ TEST_F(ExpireHistoryTest, FlushRecentURLsStarred) {
   // exists in history, this should not be a privacy problem, we only update
   // the visit counts in this case for consistency anyway.
   EXPECT_TRUE(HasFavIcon(new_url_row1.favicon_id()));
-  EXPECT_TRUE(HasThumbnail(new_url_row1.id()));
+  // TODO(sky): fix this, see comment in HasThumbnail.
+  // EXPECT_TRUE(HasThumbnail(new_url_row1.id()));
   EXPECT_TRUE(HasFavIcon(new_url_row2.favicon_id()));
-  EXPECT_TRUE(HasThumbnail(new_url_row2.id()));
+  // TODO(sky): fix this, see comment in HasThumbnail.
+  // EXPECT_TRUE(HasThumbnail(new_url_row2.id()));
 }
 
 TEST_F(ExpireHistoryTest, ArchiveHistoryBeforeUnstarred) {
diff --git a/chrome/browser/history/history.cc b/chrome/browser/history/history.cc
index bc5db7d..53a5420 100644
--- a/chrome/browser/history/history.cc
+++ b/chrome/browser/history/history.cc
@@ -127,12 +127,8 @@ HistoryService::HistoryService()
       profile_(NULL),
       backend_loaded_(false),
       bookmark_service_(NULL),
-      no_db_(false) {
-  // Is NULL when running generate_profile.
-  if (NotificationService::current()) {
-    registrar_.Add(this, NotificationType::HISTORY_URLS_DELETED,
-                   Source<Profile>(profile_));
-  }
+      no_db_(false),
+      needs_top_sites_migration_(false) {
 }
 
 HistoryService::HistoryService(Profile* profile)
@@ -140,9 +136,13 @@ HistoryService::HistoryService(Profile* profile)
       profile_(profile),
       backend_loaded_(false),
       bookmark_service_(NULL),
-      no_db_(false) {
+      no_db_(false),
+      needs_top_sites_migration_(false) {
+  DCHECK(profile_);
   registrar_.Add(this, NotificationType::HISTORY_URLS_DELETED,
                  Source<Profile>(profile_));
+  registrar_.Add(this, NotificationType::TEMPLATE_URL_REMOVED,
+                 Source<Profile>(profile_));
 }
 
 HistoryService::~HistoryService() {
@@ -609,30 +609,40 @@ HistoryService::Handle HistoryService::QueryMostVisitedURLs(
 void HistoryService::Observe(NotificationType type,
                              const NotificationSource& source,
                              const NotificationDetails& details) {
-  if (type != NotificationType::HISTORY_URLS_DELETED) {
-    NOTREACHED();
+  if (!thread_)
     return;
-  }
 
-  // Update the visited link system for deleted URLs. We will update the
-  // visited link system for added URLs as soon as we get the add
-  // notification (we don't have to wait for the backend, which allows us to
-  // be faster to update the state).
-  //
-  // For deleted URLs, we don't typically know what will be deleted since
-  // delete notifications are by time. We would also like to be more
-  // respectful of privacy and never tell the user something is gone when it
-  // isn't. Therefore, we update the delete URLs after the fact.
-  if (!profile_)
-    return;  // No profile, probably unit testing.
-  Details<history::URLsDeletedDetails> deleted_details(details);
-  VisitedLinkMaster* visited_links = profile_->GetVisitedLinkMaster();
-  if (!visited_links)
-    return;  // Nobody to update.
-  if (deleted_details->all_history)
-    visited_links->DeleteAllURLs();
-  else  // Delete individual ones.
-    visited_links->DeleteURLs(deleted_details->urls);
+  switch (type.value) {
+    case NotificationType::HISTORY_URLS_DELETED: {
+      // Update the visited link system for deleted URLs. We will update the
+      // visited link system for added URLs as soon as we get the add
+      // notification (we don't have to wait for the backend, which allows us to
+      // be faster to update the state).
+      //
+      // For deleted URLs, we don't typically know what will be deleted since
+      // delete notifications are by time. We would also like to be more
+      // respectful of privacy and never tell the user something is gone when it
+      // isn't. Therefore, we update the delete URLs after the fact.
+      if (!profile_)
+        return;  // No profile, probably unit testing.
+      Details<history::URLsDeletedDetails> deleted_details(details);
+      VisitedLinkMaster* visited_links = profile_->GetVisitedLinkMaster();
+      if (!visited_links)
+        return;  // Nobody to update.
+      if (deleted_details->all_history)
+        visited_links->DeleteAllURLs();
+      else  // Delete individual ones.
+        visited_links->DeleteURLs(deleted_details->urls);
+      break;
+    }
+
+    case NotificationType::TEMPLATE_URL_REMOVED:
+      DeleteAllSearchTermsForKeyword(*(Details<TemplateURLID>(details).ptr()));
+      break;
+
+    default:
+      NOTREACHED();
+  }
 }
 
 bool HistoryService::Init(const FilePath& history_dir,
@@ -673,6 +683,7 @@ bool HistoryService::CanAddURL(const GURL& url) {
   // typed.  Right now, however, these are marked as typed even when triggered
   // by a shortcut or menu action.
   if (url.SchemeIs(chrome::kJavaScriptScheme) ||
+      url.SchemeIs(chrome::kChromeDevToolsScheme) ||
       url.SchemeIs(chrome::kChromeUIScheme) ||
       url.SchemeIs(chrome::kViewSourceScheme) ||
       url.SchemeIs(chrome::kChromeInternalScheme))
@@ -733,6 +744,9 @@ void HistoryService::BroadcastNotifications(
   if (!g_browser_process)
     return;
 
+  if (!thread_)
+    return;
+
   // The source of all of our notifications is the profile. Note that this
   // pointer is NULL in unit tests.
   Source<Profile> source(profile_);
@@ -769,12 +783,21 @@ void HistoryService::OnDBLoaded() {
   NotificationService::current()->Notify(NotificationType::HISTORY_LOADED,
                                          Source<Profile>(profile_),
                                          Details<HistoryService>(this));
+  if (thread_ && profile_ && history::TopSites::IsEnabled()) {
+    // We don't want to force creation of TopSites.
+    history::TopSites* ts = profile_->GetTopSitesWithoutCreating();
+    if (ts)
+      ts->HistoryLoaded();
+  }
 }
 
 void HistoryService::StartTopSitesMigration() {
-  if (history::TopSites::IsEnabled()) {
-    history::TopSites* ts = profile_->GetTopSites();
-    ts->StartMigration();
+  needs_top_sites_migration_ = true;
+  if (thread_ && profile_ && history::TopSites::IsEnabled()) {
+    // We don't want to force creation of TopSites.
+    history::TopSites* ts = profile_->GetTopSitesWithoutCreating();
+    if (ts)
+      ts->MigrateFromHistory();
   }
 }
 
diff --git a/chrome/browser/history/history.h b/chrome/browser/history/history.h
index 83e629e..9d2fd20 100644
--- a/chrome/browser/history/history.h
+++ b/chrome/browser/history/history.h
@@ -118,6 +118,9 @@ class HistoryService : public CancelableRequestProvider,
   // it's finished loading.
   bool BackendLoaded();
 
+  // Returns true if the backend has finished loading.
+  bool backend_loaded() const { return backend_loaded_; }
+
   // Unloads the backend without actually shutting down the history service.
   // This can be used to temporarily reduce the browser process' memory
   // footprint.
@@ -405,7 +408,8 @@ class HistoryService : public CancelableRequestProvider,
 
   // Implemented by the caller of 'CreateDownload' below, and is called when the
   // history service has created a new entry for a download in the history db.
-  typedef Callback2<DownloadCreateInfo, int64>::Type DownloadCreateCallback;
+  typedef Callback2<const DownloadCreateInfo&, int64>::Type
+      DownloadCreateCallback;
 
   // Begins a history request to create a new persistent entry for a download.
   // 'info' contains all the download's creation state, and 'callback' runs
@@ -515,6 +519,10 @@ class HistoryService : public CancelableRequestProvider,
   virtual Handle ScheduleDBTask(HistoryDBTask* task,
                                 CancelableRequestConsumerBase* consumer);
 
+  // Returns true if top sites needs to be migrated out of history into its own
+  // db.
+  bool needs_top_sites_migration() const { return needs_top_sites_migration_; }
+
   // Testing -------------------------------------------------------------------
 
   // Designed for unit tests, this passes the given task on to the history
@@ -819,7 +827,8 @@ class HistoryService : public CancelableRequestProvider,
   // when done. We use this internal consumer for this purpose.
   CancelableRequestConsumer internal_consumer_;
 
-  // The thread used by the history service to run complicated operations
+  // The thread used by the history service to run complicated operations.
+  // |thread_| is NULL once |Cleanup| is NULL.
   base::Thread* thread_;
 
   // This class has most of the implementation and runs on the 'thread_'.
@@ -847,6 +856,9 @@ class HistoryService : public CancelableRequestProvider,
   BookmarkService* bookmark_service_;
   bool no_db_;
 
+  // True if needs top site migration.
+  bool needs_top_sites_migration_;
+
   DISALLOW_COPY_AND_ASSIGN(HistoryService);
 };
 
diff --git a/chrome/browser/history/history_backend.cc b/chrome/browser/history/history_backend.cc
index fb8e3d3..0bf6045 100644
--- a/chrome/browser/history/history_backend.cc
+++ b/chrome/browser/history/history_backend.cc
@@ -581,12 +581,9 @@ void HistoryBackend::InitImpl(const std::string& languages) {
 
   // Thumbnail database.
   thumbnail_db_.reset(new ThumbnailDatabase());
-  if (history::TopSites::IsEnabled()) {
-    // TODO(sky): once we reenable top sites this needs to be fixed.
-    // if (!db_->needs_version_18_migration()) {
+  if (history::TopSites::IsEnabled() && !db_->GetNeedsThumbnailMigration()) {
     // No convertion needed - use new filename right away.
-    // thumbnail_name = GetFaviconsFileName();
-    // }
+    thumbnail_name = GetFaviconsFileName();
   }
   if (thumbnail_db_->Init(thumbnail_name,
                           history_publisher_.get()) != sql::INIT_OK) {
@@ -599,12 +596,9 @@ void HistoryBackend::InitImpl(const std::string& languages) {
     thumbnail_db_.reset();
   }
 
-  if (history::TopSites::IsEnabled()) {
-    // TODO(sky): fix when reenabling top sites migration.
-    // if (db_->needs_version_18_migration()) {
-    // VLOG(1) << "Starting TopSites migration";
-    // delegate_->StartTopSitesMigration();
-    // }
+  if (history::TopSites::IsEnabled() && db_->GetNeedsThumbnailMigration()) {
+    VLOG(1) << "Starting TopSites migration";
+    delegate_->StartTopSitesMigration();
   }
 
   // Archived database.
@@ -1041,6 +1035,14 @@ void HistoryBackend::SetKeywordSearchTermsForURL(const GURL& url,
   }
 
   db_->SetKeywordSearchTermsForURL(url_row.id(), keyword_id, term);
+
+  // details is deleted by BroadcastNotifications.
+  KeywordSearchTermDetails* details = new KeywordSearchTermDetails;
+  details->url = url;
+  details->keyword_id = keyword_id;
+  details->term = term;
+  BroadcastNotifications(NotificationType::HISTORY_KEYWORD_SEARCH_TERM_UPDATED,
+                         details);
   ScheduleCommit();
 }
 
@@ -1341,6 +1343,16 @@ void HistoryBackend::QueryMostVisitedURLs(
   }
 
   MostVisitedURLList* result = &request->value;
+  QueryMostVisitedURLsImpl(result_count, days_back, result);
+  request->ForwardResult(QueryMostVisitedURLsRequest::TupleType(
+      request->handle(), *result));
+}
+
+void HistoryBackend::QueryMostVisitedURLsImpl(int result_count,
+                                              int days_back,
+                                              MostVisitedURLList* result) {
+  if (!db_.get())
+    return;
 
   ScopedVector<PageUsageData> data;
   db_->QuerySegmentUsage(base::Time::Now() -
@@ -1354,9 +1366,6 @@ void HistoryBackend::QueryMostVisitedURLs(
     MostVisitedURL url = MakeMostVisitedURL(*current_data, redirects);
     result->push_back(url);
   }
-
-  request->ForwardResult(QueryMostVisitedURLsRequest::TupleType(
-      request->handle(), *result));
 }
 
 void HistoryBackend::GetRedirectsFromSpecificVisit(
@@ -1516,6 +1525,19 @@ void HistoryBackend::GetPageThumbnailDirectly(
   }
 }
 
+void HistoryBackend::MigrateThumbnailsDatabase() {
+  // If there is no History DB, we can't record that the migration was done.
+  // It will be recorded on the next run.
+  if (db_.get()) {
+    // If there is no thumbnail DB, we can still record a successful migration.
+    if (thumbnail_db_.get()) {
+      thumbnail_db_->RenameAndDropThumbnails(GetThumbnailFileName(),
+                                             GetFaviconsFileName());
+    }
+    db_->ThumbnailMigrationDone();
+  }
+}
+
 bool HistoryBackend::GetThumbnailFromOlderRedirect(
     const GURL& page_url,
     std::vector<unsigned char>* data) {
@@ -2149,17 +2171,4 @@ BookmarkService* HistoryBackend::GetBookmarkService() {
   return bookmark_service_;
 }
 
-void HistoryBackend::MigrateThumbnailsDatabase() {
-  // If there is no History DB, we can't record that the migration was done.
-  // It will be recorded on the next run.
-  if (db_.get()) {
-    // If there is no thumbnail DB, we can still record a successful migration.
-    if (thumbnail_db_.get()) {
-      thumbnail_db_->RenameAndDropThumbnails(GetThumbnailFileName(),
-                                             GetFaviconsFileName());
-    }
-    db_->MigrationToTopSitesDone();
-  }
-}
-
 }  // namespace history
diff --git a/chrome/browser/history/history_backend.h b/chrome/browser/history/history_backend.h
index 3a5cea3..54cbf29 100644
--- a/chrome/browser/history/history_backend.h
+++ b/chrome/browser/history/history_backend.h
@@ -162,6 +162,11 @@ class HistoryBackend : public base::RefCountedThreadSafe<HistoryBackend>,
       int result_count,
       int days_back);
 
+  // QueryMostVisitedURLs without the request.
+  void QueryMostVisitedURLsImpl(int result_count,
+                                int days_back,
+                                MostVisitedURLList* result);
+
   // Computes the most recent URL(s) that the given canonical URL has
   // redirected to and returns true on success. There may be more than one
   // redirect in a row, so this function will fill the given array with the
diff --git a/chrome/browser/history/history_backend_unittest.cc b/chrome/browser/history/history_backend_unittest.cc
index 70760bd..ad16e9c 100644
--- a/chrome/browser/history/history_backend_unittest.cc
+++ b/chrome/browser/history/history_backend_unittest.cc
@@ -139,7 +139,8 @@ class HistoryBackendTest : public testing::Test {
     backend_->Init(std::string(), false);
   }
   virtual void TearDown() {
-    backend_->Closing();
+    if (backend_.get())
+      backend_->Closing();
     backend_ = NULL;
     mem_backend_.reset();
     file_util::Delete(test_dir_, true);
@@ -792,6 +793,8 @@ TEST_F(HistoryBackendTest, RemoveVisitsSource) {
 // Test for migration of adding visit_source table.
 TEST_F(HistoryBackendTest, MigrationVisitSource) {
   ASSERT_TRUE(backend_.get());
+  backend_->Closing();
+  backend_ = NULL;
 
   FilePath old_history_path;
   ASSERT_TRUE(PathService::Get(chrome::DIR_TEST_DATA, &old_history_path));
@@ -806,11 +809,12 @@ TEST_F(HistoryBackendTest, MigrationVisitSource) {
   FilePath new_history_file = new_history_path.Append(chrome::kHistoryFilename);
   ASSERT_TRUE(file_util::CopyFile(old_history_path, new_history_file));
 
-  backend_->Closing();
   backend_ = new HistoryBackend(new_history_path,
                                 new HistoryBackendTestDelegate(this),
                                 &bookmark_model_);
   backend_->Init(std::string(), false);
+  backend_->Closing();
+  backend_ = NULL;
 
   // Now the database should already be migrated.
   // Check version first.
diff --git a/chrome/browser/history/history_database.cc b/chrome/browser/history/history_database.cc
index 56ee054..f0c546c 100644
--- a/chrome/browser/history/history_database.cc
+++ b/chrome/browser/history/history_database.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -10,15 +10,16 @@
 #include "app/sql/transaction.h"
 #include "base/command_line.h"
 #include "base/file_util.h"
-#if defined(OS_MACOSX)
-#include "base/mac_util.h"
-#endif
 #include "base/metrics/histogram.h"
 #include "base/rand_util.h"
 #include "base/string_util.h"
 #include "chrome/browser/diagnostics/sqlite_diagnostics.h"
 #include "chrome/common/chrome_switches.h"
 
+#if defined(OS_MACOSX)
+#include "base/mac_util.h"
+#endif
+
 namespace history {
 
 namespace {
@@ -26,10 +27,14 @@ namespace {
 // Current version number. We write databases at the "current" version number,
 // but any previous version that can read the "compatible" one can make do with
 // or database without *too* many bad effects.
-static const int kCurrentVersionNumber = 19;
+static const int kCurrentVersionNumber = 20;
 static const int kCompatibleVersionNumber = 16;
 static const char kEarlyExpirationThresholdKey[] = "early_expiration_threshold";
 
+// Key in the meta table used to determine if we need to migrate thumbnails out
+// of history.
+static const char kNeedsThumbnailMigrationKey[] = "needs_thumbnail_migration";
+
 void ComputeDatabaseMetrics(const FilePath& history_name,
                             sql::Connection& db) {
   if (base::RandInt(1, 100) != 50)
@@ -114,6 +119,7 @@ sql::InitStatus HistoryDatabase::Init(const FilePath& history_name,
       !InitSegmentTables())
     return sql::INIT_FAILURE;
   CreateMainURLIndex();
+  CreateKeywordSearchTermsIndices();
   CreateSupplimentaryURLIndices();
 
   // Version check.
@@ -164,6 +170,7 @@ bool HistoryDatabase::RecreateAllTablesButURL() {
   // over parts of the URL table that weren't automatically created when the
   // temporary URL table was
   CreateSupplimentaryURLIndices();
+  CreateKeywordSearchTermsIndices();
   return true;
 }
 
@@ -173,6 +180,16 @@ void HistoryDatabase::Vacuum() {
   db_.Execute("VACUUM");
 }
 
+void HistoryDatabase::ThumbnailMigrationDone() {
+  meta_table_.SetValue(kNeedsThumbnailMigrationKey, 0);
+}
+
+bool HistoryDatabase::GetNeedsThumbnailMigration() {
+  int value = 0;
+  return (meta_table_.GetValue(kNeedsThumbnailMigrationKey, &value) &&
+          value != 0);
+}
+
 bool HistoryDatabase::SetSegmentID(VisitID visit_id, SegmentID segment_id) {
   sql::Statement s(db_.GetCachedStatement(SQL_FROM_HERE,
       "UPDATE visits SET segment_id = ? WHERE id = ?"));
@@ -289,6 +306,14 @@ sql::InitStatus HistoryDatabase::EnsureCurrentVersion(
     meta_table_.SetVersionNumber(cur_version);
   }
 
+  if (cur_version == 19) {
+    cur_version++;
+    meta_table_.SetVersionNumber(cur_version);
+    // Set a key indicating we need to migrate thumbnails. When successfull the
+    // key is removed (ThumbnailMigrationDone).
+    meta_table_.SetValue(kNeedsThumbnailMigrationKey, 1);
+  }
+
   // When the version is too old, we just try to continue anyway, there should
   // not be a released product that makes a database too old for us to handle.
   LOG_IF(WARNING, cur_version < GetCurrentVersion()) <<
@@ -322,8 +347,4 @@ void HistoryDatabase::MigrateTimeEpoch() {
 }
 #endif
 
-void HistoryDatabase::MigrationToTopSitesDone() {
-  // TODO(sky): implement me.
-}
-
 }  // namespace history
diff --git a/chrome/browser/history/history_database.h b/chrome/browser/history/history_database.h
index fe74e89..1f0c219 100644
--- a/chrome/browser/history/history_database.h
+++ b/chrome/browser/history/history_database.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -123,8 +123,11 @@ class HistoryDatabase : public DownloadDatabase,
     return needs_version_17_migration_;
   }
 
-  // Update the database version after the TopSites migration.
-  void MigrationToTopSitesDone();
+  // Marks the database as no longer needing migration.
+  void ThumbnailMigrationDone();
+
+  // Returns true if thumbnails needs to be migrated.
+  bool GetNeedsThumbnailMigration();
 
   // Visit table functions ----------------------------------------------------
 
diff --git a/chrome/browser/history/history_notifications.cc b/chrome/browser/history/history_notifications.cc
index c846eaf..0fdfa94 100644
--- a/chrome/browser/history/history_notifications.cc
+++ b/chrome/browser/history/history_notifications.cc
@@ -28,4 +28,8 @@ FavIconChangeDetails::FavIconChangeDetails() {}
 
 FavIconChangeDetails::~FavIconChangeDetails() {}
 
+KeywordSearchTermDetails::KeywordSearchTermDetails() : keyword_id(0) {}
+
+KeywordSearchTermDetails::~KeywordSearchTermDetails() {}
+
 }  // namespace history
diff --git a/chrome/browser/history/history_notifications.h b/chrome/browser/history/history_notifications.h
index 7a2404c..0d82135 100644
--- a/chrome/browser/history/history_notifications.h
+++ b/chrome/browser/history/history_notifications.h
@@ -13,6 +13,7 @@
 
 #include "googleurl/src/gurl.h"
 #include "chrome/browser/history/history_types.h"
+#include "chrome/browser/search_engines/template_url_id.h"
 
 namespace history {
 
@@ -27,7 +28,7 @@ struct HistoryDetails {
 // Details for HISTORY_URL_VISITED.
 struct URLVisitedDetails : public HistoryDetails {
   URLVisitedDetails();
-  ~URLVisitedDetails();
+  virtual ~URLVisitedDetails();
 
   PageTransition::Type transition;
   URLRow row;
@@ -42,7 +43,7 @@ struct URLVisitedDetails : public HistoryDetails {
 // Details for NOTIFY_HISTORY_TYPED_URLS_MODIFIED.
 struct URLsModifiedDetails : public HistoryDetails {
   URLsModifiedDetails();
-  ~URLsModifiedDetails();
+  virtual ~URLsModifiedDetails();
 
   // Lists the information for each of the URLs affected.
   std::vector<URLRow> changed_urls;
@@ -51,7 +52,7 @@ struct URLsModifiedDetails : public HistoryDetails {
 // Details for NOTIFY_HISTORY_URLS_DELETED.
 struct URLsDeletedDetails : public HistoryDetails {
   URLsDeletedDetails();
-  ~URLsDeletedDetails();
+  virtual ~URLsDeletedDetails();
 
   // Set when all history was deleted. False means just a subset was deleted.
   bool all_history;
@@ -65,7 +66,7 @@ struct URLsDeletedDetails : public HistoryDetails {
 // Details for NOTIFY_URLS_STARRED.
 struct URLsStarredDetails : public HistoryDetails {
   explicit URLsStarredDetails(bool being_starred);
-  ~URLsStarredDetails();
+  virtual ~URLsStarredDetails();
 
   // The new starred state of the list of URLs. True when they are being
   // starred, false when they are being unstarred.
@@ -78,11 +79,21 @@ struct URLsStarredDetails : public HistoryDetails {
 // Details for NOTIFY_FAVICON_CHANGED.
 struct FavIconChangeDetails : public HistoryDetails {
   FavIconChangeDetails();
-  ~FavIconChangeDetails();
+  virtual ~FavIconChangeDetails();
 
   std::set<GURL> urls;
 };
 
+// Details for HISTORY_KEYWORD_SEARCH_TERM_UPDATED.
+struct KeywordSearchTermDetails : public HistoryDetails {
+  KeywordSearchTermDetails();
+  ~KeywordSearchTermDetails();
+
+  GURL url;
+  TemplateURLID keyword_id;
+  string16 term;
+};
+
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_HISTORY_NOTIFICATIONS_H__
diff --git a/chrome/browser/history/history_types.cc b/chrome/browser/history/history_types.cc
index 408bb93..eebe5a7 100644
--- a/chrome/browser/history/history_types.cc
+++ b/chrome/browser/history/history_types.cc
@@ -366,4 +366,7 @@ HistoryAddPageArgs* HistoryAddPageArgs::Clone() const {
       visit_source, did_replace_entry);
 }
 
+MostVisitedThumbnails::MostVisitedThumbnails() {
+}
+
 }  // namespace history
diff --git a/chrome/browser/history/history_types.h b/chrome/browser/history/history_types.h
index 831c0b0..536064a 100644
--- a/chrome/browser/history/history_types.h
+++ b/chrome/browser/history/history_types.h
@@ -544,20 +544,6 @@ struct MostVisitedURL {
   }
 };
 
-// Used by TopSites to store the thumbnails.
-struct Images {
-  Images();
-  ~Images();
-
-  scoped_refptr<RefCountedBytes> thumbnail;
-  ThumbnailScore thumbnail_score;
-
-  // TODO(brettw): this will eventually store the favicon.
-  // scoped_refptr<RefCountedBytes> favicon;
-};
-
-typedef std::vector<MostVisitedURL> MostVisitedURLList;
-
 // Navigation -----------------------------------------------------------------
 
 // Marshalling structure for AddPage.
@@ -598,6 +584,61 @@ class HistoryAddPageArgs
   DISALLOW_COPY_AND_ASSIGN(HistoryAddPageArgs);
 };
 
+// TopSites -------------------------------------------------------------------
+
+typedef std::vector<MostVisitedURL> MostVisitedURLList;
+
+// Used by TopSites to store the thumbnails.
+struct Images {
+  Images();
+  ~Images();
+
+  scoped_refptr<RefCountedBytes> thumbnail;
+  ThumbnailScore thumbnail_score;
+
+  // TODO(brettw): this will eventually store the favicon.
+  // scoped_refptr<RefCountedBytes> favicon;
+};
+
+typedef std::vector<MostVisitedURL> MostVisitedURLList;
+
+struct MostVisitedURLWithRank {
+  MostVisitedURL url;
+  int rank;
+};
+
+typedef std::vector<MostVisitedURLWithRank> MostVisitedURLWithRankList;
+
+struct TopSitesDelta {
+  MostVisitedURLList deleted;
+  MostVisitedURLWithRankList added;
+  MostVisitedURLWithRankList moved;
+};
+
+typedef std::map<GURL, scoped_refptr<RefCountedBytes> > URLToThumbnailMap;
+
+// Used when migrating most visited thumbnails out of history and into topsites.
+struct ThumbnailMigration {
+  MostVisitedURLList most_visited;
+  URLToThumbnailMap url_to_thumbnail_map;
+};
+
+typedef std::map<GURL, Images> URLToImagesMap;
+
+class MostVisitedThumbnails
+    : public base::RefCountedThreadSafe<MostVisitedThumbnails> {
+ public:
+  MostVisitedThumbnails();
+
+  MostVisitedURLList most_visited;
+  URLToImagesMap url_to_images_map;
+
+ private:
+  friend class base::RefCountedThreadSafe<MostVisitedThumbnails>;
+
+  DISALLOW_COPY_AND_ASSIGN(MostVisitedThumbnails);
+};
+
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_HISTORY_TYPES_H_
diff --git a/chrome/browser/history/in_memory_database.cc b/chrome/browser/history/in_memory_database.cc
index 3227a7a..168a544 100644
--- a/chrome/browser/history/in_memory_database.cc
+++ b/chrome/browser/history/in_memory_database.cc
@@ -41,6 +41,13 @@ bool InMemoryDatabase::InitDB() {
     return false;
   }
 
+  // Create the keyword search terms table.
+  if (!InitKeywordSearchTermsTable()) {
+    NOTREACHED() << "Unable to create keyword search terms";
+    db_.Close();
+    return false;
+  }
+
   return true;
 }
 
@@ -51,6 +58,7 @@ bool InMemoryDatabase::InitFromScratch() {
   // InitDB doesn't create the index so in the disk-loading case, it can be
   // added afterwards.
   CreateMainURLIndex();
+  CreateKeywordSearchTermsIndices();
   return true;
 }
 
@@ -87,6 +95,36 @@ bool InMemoryDatabase::InitFromDisk(const FilePath& history_name) {
                              end_load - begin_load);
   UMA_HISTOGRAM_COUNTS("History.InMemoryDBItemCount", db_.GetLastChangeCount());
 
+  // Insert keyword search related URLs.
+  begin_load = base::TimeTicks::Now();
+  if (!db_.Execute(
+      "INSERT INTO urls SELECT u.id, u.url, u.title, u.visit_count, "
+      "u.typed_count, u.last_visit_time, u.hidden, u.favicon_id "
+      "FROM history.urls u JOIN history.keyword_search_terms kst "
+      "WHERE u.typed_count = 0 AND u.id = kst.url_id")) {
+    // Unable to get data from the history database. This is OK, the file may
+    // just not exist yet.
+  }
+  end_load = base::TimeTicks::Now();
+  UMA_HISTOGRAM_MEDIUM_TIMES("History.InMemoryDBKeywordURLPopulate",
+                             end_load - begin_load);
+  UMA_HISTOGRAM_COUNTS("History.InMemoryDBKeywordURLItemCount",
+                       db_.GetLastChangeCount());
+
+  // Copy search terms to memory.
+  begin_load = base::TimeTicks::Now();
+  if (!db_.Execute(
+      "INSERT INTO keyword_search_terms SELECT * FROM "
+      "history.keyword_search_terms")) {
+    // Unable to get data from the history database. This is OK, the file may
+    // just not exist yet.
+  }
+  end_load = base::TimeTicks::Now();
+  UMA_HISTOGRAM_MEDIUM_TIMES("History.InMemoryDBKeywordTermsPopulate",
+                             end_load - begin_load);
+  UMA_HISTOGRAM_COUNTS("History.InMemoryDBKeywordTermsCount",
+                       db_.GetLastChangeCount());
+
   // Detach from the history database on disk.
   if (!db_.Execute("DETACH history")) {
     NOTREACHED() << "Unable to detach from history database.";
@@ -96,6 +134,7 @@ bool InMemoryDatabase::InitFromDisk(const FilePath& history_name) {
   // Index the table, this is faster than creating the index first and then
   // inserting into it.
   CreateMainURLIndex();
+  CreateKeywordSearchTermsIndices();
 
   return true;
 }
diff --git a/chrome/browser/history/in_memory_history_backend.cc b/chrome/browser/history/in_memory_history_backend.cc
index 6827a78..be82f58 100644
--- a/chrome/browser/history/in_memory_history_backend.cc
+++ b/chrome/browser/history/in_memory_history_backend.cc
@@ -72,6 +72,9 @@ void InMemoryHistoryBackend::AttachToHistoryService(Profile* profile) {
   registrar_.Add(this, NotificationType::HISTORY_URL_VISITED, source);
   registrar_.Add(this, NotificationType::HISTORY_TYPED_URLS_MODIFIED, source);
   registrar_.Add(this, NotificationType::HISTORY_URLS_DELETED, source);
+  registrar_.Add(this, NotificationType::HISTORY_KEYWORD_SEARCH_TERM_UPDATED,
+                 source);
+  registrar_.Add(this, NotificationType::TEMPLATE_URL_REMOVED, source);
 }
 
 void InMemoryHistoryBackend::Observe(NotificationType type,
@@ -80,13 +83,20 @@ void InMemoryHistoryBackend::Observe(NotificationType type,
   switch (type.value) {
     case NotificationType::HISTORY_URL_VISITED: {
       Details<history::URLVisitedDetails> visited_details(details);
-      if (visited_details->row.typed_count() > 0) {
+      PageTransition::Type primary_type =
+          PageTransition::StripQualifier(visited_details->transition);
+      if (visited_details->row.typed_count() > 0 ||
+          primary_type == PageTransition::KEYWORD) {
         URLsModifiedDetails modified_details;
         modified_details.changed_urls.push_back(visited_details->row);
         OnTypedURLsModified(modified_details);
       }
       break;
     }
+    case NotificationType::HISTORY_KEYWORD_SEARCH_TERM_UPDATED:
+      OnKeywordSearchTermUpdated(
+          *Details<history::KeywordSearchTermDetails>(details).ptr());
+      break;
     case NotificationType::HISTORY_TYPED_URLS_MODIFIED:
       OnTypedURLsModified(
           *Details<history::URLsModifiedDetails>(details).ptr());
@@ -94,6 +104,10 @@ void InMemoryHistoryBackend::Observe(NotificationType type,
     case NotificationType::HISTORY_URLS_DELETED:
       OnURLsDeleted(*Details<history::URLsDeletedDetails>(details).ptr());
       break;
+    case NotificationType::TEMPLATE_URL_REMOVED:
+      db_->DeleteAllSearchTermsForKeyword(
+          *(Details<TemplateURLID>(details).ptr()));
+      break;
     default:
       // For simplicity, the unit tests send us all notifications, even when
       // we haven't registered for them, so don't assert here.
@@ -145,4 +159,27 @@ void InMemoryHistoryBackend::OnURLsDeleted(const URLsDeletedDetails& details) {
   }
 }
 
+void InMemoryHistoryBackend::OnKeywordSearchTermUpdated(
+    const KeywordSearchTermDetails& details) {
+  // The url won't exist for new search terms (as the user hasn't typed it), so
+  // we force it to be added. If we end up adding a URL it won't be
+  // autocompleted as the typed count is 0.
+  URLRow url_row;
+  URLID url_id;
+  if (!db_->GetRowForURL(details.url, &url_row)) {
+    // Because this row won't have a typed count the title and other stuff
+    // doesn't matter. If the user ends up typing the url we'll update the title
+    // in OnTypedURLsModified.
+    URLRow new_row(details.url);
+    new_row.set_last_visit(base::Time::Now());
+    url_id = db_->AddURL(new_row);
+    if (!url_id)
+      return;  // Error adding.
+  } else {
+    url_id = url_row.id();
+  }
+
+  db_->SetKeywordSearchTermsForURL(url_id, details.keyword_id, details.term);
+}
+
 }  // namespace history
diff --git a/chrome/browser/history/in_memory_history_backend.h b/chrome/browser/history/in_memory_history_backend.h
index 4fdc3a5..c775800 100644
--- a/chrome/browser/history/in_memory_history_backend.h
+++ b/chrome/browser/history/in_memory_history_backend.h
@@ -30,6 +30,7 @@ namespace history {
 
 class InMemoryDatabase;
 class InMemoryURLIndex;
+struct KeywordSearchTermDetails;
 class URLDatabase;
 struct URLsDeletedDetails;
 struct URLsModifiedDetails;
@@ -73,6 +74,9 @@ class InMemoryHistoryBackend : public NotificationObserver {
   // Handler for NOTIFY_HISTORY_URLS_DELETED.
   void OnURLsDeleted(const URLsDeletedDetails& details);
 
+  // Handler for HISTORY_KEYWORD_SEARCH_TERM_UPDATED.
+  void OnKeywordSearchTermUpdated(const KeywordSearchTermDetails& details);
+
   NotificationRegistrar registrar_;
 
   scoped_ptr<InMemoryDatabase> db_;
diff --git a/chrome/browser/history/in_memory_url_index.cc b/chrome/browser/history/in_memory_url_index.cc
index 654afdc..98c2acd 100644
--- a/chrome/browser/history/in_memory_url_index.cc
+++ b/chrome/browser/history/in_memory_url_index.cc
@@ -34,7 +34,9 @@ ScoredHistoryMatch::ScoredHistoryMatch(const URLRow& url_info,
 }
 
 struct InMemoryURLIndex::TermCharWordSet {
-  TermCharWordSet(Char16Set char_set, WordIDSet word_id_set, bool used)
+  TermCharWordSet(const Char16Set& char_set,
+                  const WordIDSet& word_id_set,
+                  bool used)
       : char_set_(char_set),
         word_id_set_(word_id_set),
         used_(used) {}
@@ -81,7 +83,7 @@ bool InMemoryURLIndex::Init(history::URLDatabase* history_db,
   return true;
 }
 
-bool InMemoryURLIndex::IndexRow(URLRow row) {
+bool InMemoryURLIndex::IndexRow(const URLRow& row) {
   const GURL& gurl(row.url());
   string16 url(net::FormatUrl(gurl, languages_,
       net::kFormatUrlOmitUsernamePassword,
diff --git a/chrome/browser/history/in_memory_url_index.h b/chrome/browser/history/in_memory_url_index.h
index a2ac0f3..81336f1 100644
--- a/chrome/browser/history/in_memory_url_index.h
+++ b/chrome/browser/history/in_memory_url_index.h
@@ -159,7 +159,7 @@ class InMemoryURLIndex {
   // URL History indexing support functions.
 
   // Index one URL history item.
-  bool IndexRow(URLRow row);
+  bool IndexRow(const URLRow& row);
 
   // Break a string down into its individual characters.
   // Note that this is temporarily intended to work on a single word, but
diff --git a/chrome/browser/history/text_database.cc b/chrome/browser/history/text_database.cc
index 84367d3..60aa7fd 100644
--- a/chrome/browser/history/text_database.cc
+++ b/chrome/browser/history/text_database.cc
@@ -112,8 +112,8 @@ TextDatabase::DBIdent TextDatabase::FileNameToID(const FilePath& file_path) {
   }
 
   int year, month;
-  base::StringToInt(suffix.substr(0, 4), &year);
-  base::StringToInt(suffix.substr(5, 2), &month);
+  base::StringToInt(suffix.begin(), suffix.begin() + 4, &year);
+  base::StringToInt(suffix.begin() + 5, suffix.begin() + 7, &month);
 
   return year * 100 + month;
 }
diff --git a/chrome/browser/history/thumbnail_database.cc b/chrome/browser/history/thumbnail_database.cc
index 9cd3f9c..e1054ac 100644
--- a/chrome/browser/history/thumbnail_database.cc
+++ b/chrome/browser/history/thumbnail_database.cc
@@ -104,21 +104,10 @@ sql::InitStatus ThumbnailDatabase::OpenDatabase(sql::Connection* db,
   // Set the exceptional sqlite error handler.
   db->set_error_delegate(GetErrorHandlerForThumbnailDb());
 
-  // Set the database page size to something  larger to give us
-  // better performance (we're typically seek rather than bandwidth limited).
-  // This only has an effect before any tables have been created, otherwise
-  // this is a NOP. Must be a power of 2 and a max of 8192. We use a bigger
-  // one because we're storing larger data (4-16K) in it, so we want a few
-  // blocks per element.
-  db->set_page_size(4096);
-
-  // The UI is generally designed to work well when the thumbnail database is
-  // slow, so we can tolerate much less caching. The file is also very large
-  // and so caching won't save a significant percentage of it for us,
-  // reducing the benefit of caching in the first place. With the default cache
-  // size of 2000 pages, it will take >8MB of memory, so reducing it can be a
-  // big savings.
-  db->set_cache_size(64);
+  // Thumbnails db now only stores favicons, so we don't need that big a page
+  // size or cache.
+  db->set_page_size(2048);
+  db->set_cache_size(32);
 
   // Run the database in exclusive mode. Nobody else should be accessing the
   // database while we're running, and this will give somewhat improved perf.
@@ -310,7 +299,6 @@ bool ThumbnailDatabase::GetPageThumbnail(URLID id,
 
 bool ThumbnailDatabase::DeleteThumbnail(URLID id) {
   if (use_top_sites_) {
-    LOG(WARNING) << "Use TopSites instead.";
     return true;  // Not possible after migration to TopSites.
   }
 
diff --git a/chrome/browser/history/top_sites.cc b/chrome/browser/history/top_sites.cc
index 31ce4ac..8bdfe34 100644
--- a/chrome/browser/history/top_sites.cc
+++ b/chrome/browser/history/top_sites.cc
@@ -5,10 +5,10 @@
 #include "chrome/browser/history/top_sites.h"
 
 #include <algorithm>
+#include <set>
 
 #include "app/l10n_util.h"
 #include "base/command_line.h"
-#include "base/file_util.h"
 #include "base/logging.h"
 #include "base/md5.h"
 #include "base/string_util.h"
@@ -16,14 +16,17 @@
 #include "base/values.h"
 #include "chrome/browser/browser_thread.h"
 #include "chrome/browser/dom_ui/most_visited_handler.h"
+#include "chrome/browser/history/history_backend.h"
 #include "chrome/browser/history/history_notifications.h"
 #include "chrome/browser/history/page_usage_data.h"
-#include "chrome/browser/history/top_sites_database.h"
+#include "chrome/browser/history/top_sites_backend.h"
+#include "chrome/browser/history/top_sites_cache.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/profile.h"
 #include "chrome/browser/tab_contents/navigation_controller.h"
 #include "chrome/browser/tab_contents/navigation_entry.h"
 #include "chrome/common/chrome_switches.h"
+#include "chrome/common/notification_service.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/thumbnail_score.h"
 #include "gfx/codec/jpeg_codec.h"
@@ -36,6 +39,11 @@ namespace history {
 
 // How many top sites to store in the cache.
 static const size_t kTopSitesNumber = 20;
+
+// Max number of temporary images we'll cache. See comment above
+// temp_images_ for details.
+static const size_t kMaxTempTopImages = 8;
+
 static const size_t kTopSitesShown = 8;
 static const int kDaysOfHistory = 90;
 // Time from startup to first HistoryService query.
@@ -44,14 +52,91 @@ static const int64 kUpdateIntervalSecs = 15;
 static const int64 kMinUpdateIntervalMinutes = 1;
 static const int64 kMaxUpdateIntervalMinutes = 60;
 
+// IDs of the sites we force into top sites.
+static const int kPrepopulatePageIDs[] =
+    { IDS_CHROME_WELCOME_URL, IDS_THEMES_GALLERY_URL };
+
+// Favicons of the sites we force into top sites.
+static const char kPrepopulateFaviconURLs[][54] =
+    { "chrome://theme/IDR_NEWTAB_CHROME_WELCOME_PAGE_FAVICON",
+      "chrome://theme/IDR_NEWTAB_THEMES_GALLERY_FAVICON" };
+
+static const int kPrepopulateTitleIDs[] =
+    { IDS_NEW_TAB_CHROME_WELCOME_PAGE_TITLE,
+      IDS_NEW_TAB_THEMES_GALLERY_PAGE_TITLE };
+
+namespace {
+
+// HistoryDBTask used during migration of thumbnails from history to top sites.
+// When run on the history thread it collects the top sites and the
+// corresponding thumbnails. When run back on the ui thread it calls into
+// TopSites::FinishHistoryMigration.
+class LoadThumbnailsFromHistoryTask : public HistoryDBTask {
+ public:
+  LoadThumbnailsFromHistoryTask(TopSites* top_sites,
+                                int result_count)
+      : top_sites_(top_sites),
+        result_count_(result_count) {
+    // l10n_util isn't thread safe, so cache for use on the db thread.
+    ignore_urls_.insert(l10n_util::GetStringUTF8(IDS_CHROME_WELCOME_URL));
+    ignore_urls_.insert(l10n_util::GetStringUTF8(IDS_THEMES_GALLERY_URL));
+  }
+
+  virtual bool RunOnDBThread(history::HistoryBackend* backend,
+                             history::HistoryDatabase* db) {
+    // Get the most visited urls.
+    backend->QueryMostVisitedURLsImpl(result_count_,
+                                      kDaysOfHistory,
+                                      &data_.most_visited);
+
+    // And fetch the thumbnails.
+    for (size_t i = 0; i < data_.most_visited.size(); ++i) {
+      const GURL& url = data_.most_visited[i].url;
+      if (ShouldFetchThumbnailFor(url)) {
+        scoped_refptr<RefCountedBytes> data;
+        backend->GetPageThumbnailDirectly(url, &data);
+        data_.url_to_thumbnail_map[url] = data;
+      }
+    }
+    return true;
+  }
+
+  virtual void DoneRunOnMainThread() {
+    top_sites_->FinishHistoryMigration(data_);
+  }
+
+ private:
+  bool ShouldFetchThumbnailFor(const GURL& url) {
+    return ignore_urls_.find(url.spec()) == ignore_urls_.end();
+  }
+
+  // Set of URLs we don't load thumbnails for. This is created on the UI thread
+  // and used on the history thread.
+  std::set<std::string> ignore_urls_;
+
+  scoped_refptr<TopSites> top_sites_;
+
+  // Number of results to request from history.
+  const int result_count_;
+
+  ThumbnailMigration data_;
+
+  DISALLOW_COPY_AND_ASSIGN(LoadThumbnailsFromHistoryTask);
+};
+
+}  // namespace
 
-TopSites::TopSites(Profile* profile) : profile_(profile),
-                                       mock_history_service_(NULL),
-                                       last_num_urls_changed_(0),
-                                       migration_in_progress_(false),
-                                       waiting_for_results_(true),
-                                       blacklist_(NULL),
-                                       pinned_urls_(NULL) {
+TopSites::TopSites(Profile* profile)
+    : backend_(new TopSitesBackend()),
+      cache_(new TopSitesCache()),
+      thread_safe_cache_(new TopSitesCache()),
+      profile_(profile),
+      last_num_urls_changed_(0),
+      blacklist_(NULL),
+      pinned_urls_(NULL),
+      history_state_(HISTORY_LOADING),
+      top_sites_state_(TOP_SITES_LOADING),
+      loaded_(false) {
   if (!profile_)
     return;
 
@@ -70,61 +155,42 @@ TopSites::TopSites(Profile* profile) : profile_(profile),
 
 // static
 bool TopSites::IsEnabled() {
-  return CommandLine::ForCurrentProcess()->HasSwitch(switches::kEnableTopSites);
-}
-
-TopSites::~TopSites() {
-  timer_.Stop();
+  std::string switch_value =
+      CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+          switches::kEnableTopSites);
+  return switch_value.empty() || switch_value == "true";
 }
 
 void TopSites::Init(const FilePath& db_name) {
-  db_path_ = db_name;
-  db_.reset(new TopSitesDatabaseImpl());
-  if (!db_->Init(db_name)) {
-    NOTREACHED() << "Failed to initialize database.";
-    return;
-  }
+  backend_->Init(db_name);
+  backend_->GetMostVisitedThumbnails(
+      &cancelable_consumer_,
+      NewCallback(this, &TopSites::OnGotMostVisitedThumbnails));
 
-  BrowserThread::PostTask(BrowserThread::DB, FROM_HERE, NewRunnableMethod(
-      this, &TopSites::ReadDatabase));
-
-  // Start the one-shot timer.
-  timer_.Start(base::TimeDelta::FromSeconds(kUpdateIntervalSecs), this,
-               &TopSites::StartQueryForMostVisited);
-}
-
-void TopSites::ReadDatabase() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
-  std::map<GURL, Images> thumbnails;
-
-  DCHECK(db_.get());
-  MostVisitedURLList top_urls;
-  db_->GetPageThumbnails(&top_urls, &thumbnails);
-  MostVisitedURLList copy(top_urls);  // StoreMostVisited destroys the list.
-  StoreMostVisited(&top_urls);
-  if (AddPrepopulatedPages(&copy))
-    UpdateMostVisited(copy);
-
-  AutoLock lock(lock_);
-  for (size_t i = 0; i < top_sites_.size(); i++) {
-    GURL url = top_sites_[i].url;
-    Images thumbnail = thumbnails[url];
-    if (thumbnail.thumbnail.get() && thumbnail.thumbnail->size()) {
-      SetPageThumbnailNoDB(url, thumbnail.thumbnail,
-                           thumbnail.thumbnail_score);
-    }
+  // History may have already finished loading by the time we're created.
+  HistoryService* history = profile_->GetHistoryServiceWithoutCreating();
+  if (history && history->backend_loaded()) {
+    if (history->needs_top_sites_migration())
+      MigrateFromHistory();
+    else
+      history_state_ = HISTORY_LOADED;
   }
 }
 
-// Public function that encodes the bitmap into RefCountedBytes and
-// updates the database.
 bool TopSites::SetPageThumbnail(const GURL& url,
                                 const SkBitmap& thumbnail,
                                 const ThumbnailScore& score) {
-  AutoLock lock(lock_);
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  if (!loaded_) {
+    // TODO(sky): I need to cache these and apply them after the load
+    // completes.
+    return false;
+  }
+
   bool add_temp_thumbnail = false;
-  if (canonical_urls_.find(url) == canonical_urls_.end()) {
-    if (top_sites_.size() < kTopSitesNumber) {
+  if (!cache_->IsKnownURL(url)) {
+    if (cache_->top_sites().size() < kTopSitesNumber) {
       add_temp_thumbnail = true;
     } else {
       return false;  // This URL is not known to us.
@@ -134,18 +200,14 @@ bool TopSites::SetPageThumbnail(const GURL& url,
   if (!HistoryService::CanAddURL(url))
     return false;  // It's not a real webpage.
 
-  scoped_refptr<RefCountedBytes> thumbnail_data = new RefCountedBytes;
-  SkAutoLockPixels thumbnail_lock(thumbnail);
-  bool encoded = gfx::JPEGCodec::Encode(
-      reinterpret_cast<unsigned char*>(thumbnail.getAddr32(0, 0)),
-      gfx::JPEGCodec::FORMAT_SkBitmap, thumbnail.width(),
-      thumbnail.height(),
-      static_cast<int>(thumbnail.rowBytes()), 90,
-      &thumbnail_data->data);
-  if (!encoded)
+  scoped_refptr<RefCountedBytes> thumbnail_data;
+  if (!EncodeBitmap(thumbnail, &thumbnail_data))
     return false;
 
   if (add_temp_thumbnail) {
+    // Always remove the existing entry and then add it back. That way if we end
+    // up with too many temp thumbnails we'll prune the oldest first.
+    RemoveTemporaryThumbnailByURL(url);
     AddTemporaryThumbnail(url, thumbnail_data, score);
     return true;
   }
@@ -153,59 +215,243 @@ bool TopSites::SetPageThumbnail(const GURL& url,
   return SetPageThumbnailEncoded(url, thumbnail_data, score);
 }
 
-bool TopSites::SetPageThumbnailEncoded(const GURL& url,
-                                       const RefCountedBytes* thumbnail,
-                                       const ThumbnailScore& score) {
-  lock_.AssertAcquired();
-  if (!SetPageThumbnailNoDB(url, thumbnail, score))
-    return false;
+void TopSites::GetMostVisitedURLs(CancelableRequestConsumer* consumer,
+                                  GetTopSitesCallback* callback) {
+  // WARNING: this may be invoked on any thread.
+  scoped_refptr<CancelableRequest<GetTopSitesCallback> > request(
+      new CancelableRequest<GetTopSitesCallback>(callback));
+  // This ensures cancelation of requests when either the consumer or the
+  // provider is deleted. Deletion of requests is also guaranteed.
+  AddRequest(request, consumer);
+  MostVisitedURLList filtered_urls;
+  {
+    AutoLock lock(lock_);
+    if (!loaded_) {
+      // A request came in before we finished loading. Put the request in
+      // pending_callbacks_ and we'll notify it when we finish loading.
+      pending_callbacks_.insert(request);
+      return;
+    }
 
-  // Update the database.
-  if (!db_.get())
-    return true;
-  std::map<GURL, size_t>::iterator found = canonical_urls_.find(url);
-  if (found == canonical_urls_.end())
-    return false;
-  size_t index = found->second;
+    filtered_urls = thread_safe_cache_->top_sites();
+  }
+  request->ForwardResult(GetTopSitesCallback::TupleType(filtered_urls));
+}
 
-  MostVisitedURL& most_visited = top_sites_[index];
-  BrowserThread::PostTask(BrowserThread::DB, FROM_HERE, NewRunnableMethod(
-      this, &TopSites::WriteThumbnailToDB,
-      most_visited, index, top_images_[most_visited.url]));
-  return true;
+bool TopSites::GetPageThumbnail(const GURL& url,
+                                scoped_refptr<RefCountedBytes>* bytes) {
+  // WARNING: this may be invoked on any thread.
+  AutoLock lock(lock_);
+  return thread_safe_cache_->GetPageThumbnail(url, bytes);
+}
+
+// Returns the index of |url| in |urls|, or -1 if not found.
+static int IndexOf(const MostVisitedURLList& urls, const GURL& url) {
+  for (size_t i = 0; i < urls.size(); i++) {
+    if (urls[i].url == url)
+      return i;
+  }
+  return -1;
 }
 
-void TopSites::WriteThumbnailToDB(const MostVisitedURL& url,
-                                  int url_rank,
-                                  const Images& thumbnail) {
-  DCHECK(db_.get());
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
-  db_->SetPageThumbnail(url, url_rank, thumbnail);
+void TopSites::MigrateFromHistory() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK_EQ(history_state_, HISTORY_LOADING);
+
+  history_state_ = HISTORY_MIGRATING;
+  profile_->GetHistoryService(Profile::EXPLICIT_ACCESS)->ScheduleDBTask(
+      new LoadThumbnailsFromHistoryTask(
+          this,
+          num_results_to_request_from_history()),
+      &cancelable_consumer_);
+  MigratePinnedURLs();
 }
 
-// private
-bool TopSites::SetPageThumbnailNoDB(const GURL& url,
-                                    const RefCountedBytes* thumbnail_data,
-                                    const ThumbnailScore& score) {
-  lock_.AssertAcquired();
+void TopSites::FinishHistoryMigration(const ThumbnailMigration& data) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK_EQ(history_state_, HISTORY_MIGRATING);
 
-  std::map<GURL, size_t>::iterator found = canonical_urls_.find(url);
-  if (found == canonical_urls_.end()) {
-    if (top_sites_.size() >= kTopSitesNumber)
-      return false;  // This URL is not known to us.
+  history_state_ = HISTORY_LOADED;
 
-    // We don't have enough Top Sites - add this one too.
-    MostVisitedURL mv;
-    mv.url = url;
-    mv.redirects.push_back(url);
-    top_sites_.push_back(mv);
-    size_t index = top_sites_.size() - 1;
-    StoreRedirectChain(top_sites_[index].redirects, index);
-    found = canonical_urls_.find(url);
+  SetTopSites(data.most_visited);
+
+  for (size_t i = 0; i < data.most_visited.size(); ++i) {
+    URLToThumbnailMap::const_iterator image_i =
+        data.url_to_thumbnail_map.find(data.most_visited[i].url);
+    if (image_i != data.url_to_thumbnail_map.end()) {
+      SetPageThumbnailEncoded(data.most_visited[i].url,
+                              image_i->second,
+                              ThumbnailScore());
+    }
   }
 
-  MostVisitedURL& most_visited = top_sites_[found->second];
-  Images& image = top_images_[most_visited.url];
+  MoveStateToLoaded();
+
+  ResetThreadSafeImageCache();
+
+  // We've scheduled all the thumbnails and top sites to be written to the top
+  // sites db, but it hasn't happened yet. Schedule a request on the db thread
+  // that notifies us when done. When done we'll know everything was written and
+  // we can tell history to finish its part of migration.
+  backend_->DoEmptyRequest(
+      &cancelable_consumer_,
+      NewCallback(this, &TopSites::OnHistoryMigrationWrittenToDisk));
+}
+
+void TopSites::HistoryLoaded() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK_NE(history_state_, HISTORY_LOADED);
+
+  if (history_state_ != HISTORY_MIGRATING) {
+    // No migration from history is needed.
+    history_state_ = HISTORY_LOADED;
+    if (top_sites_state_ == TOP_SITES_LOADED_WAITING_FOR_HISTORY) {
+      // TopSites thought it needed migration, but it really didn't. This
+      // typically happens the first time a profile is run with Top Sites
+      // enabled
+      SetTopSites(MostVisitedURLList());
+      MoveStateToLoaded();
+    }
+  }
+}
+
+bool TopSites::HasBlacklistedItems() const {
+  return !blacklist_->empty();
+}
+
+void TopSites::AddBlacklistedURL(const GURL& url) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  RemovePinnedURL(url);
+  Value* dummy = Value::CreateNullValue();
+  blacklist_->SetWithoutPathExpansion(GetURLHash(url), dummy);
+
+  ResetThreadSafeCache();
+}
+
+void TopSites::RemoveBlacklistedURL(const GURL& url) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  blacklist_->RemoveWithoutPathExpansion(GetURLHash(url), NULL);
+  ResetThreadSafeCache();
+}
+
+bool TopSites::IsBlacklisted(const GURL& url) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  return blacklist_->HasKey(GetURLHash(url));
+}
+
+void TopSites::ClearBlacklistedURLs() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  blacklist_->Clear();
+  ResetThreadSafeCache();
+}
+
+void TopSites::AddPinnedURL(const GURL& url, size_t pinned_index) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  GURL old;
+  if (GetPinnedURLAtIndex(pinned_index, &old))
+    RemovePinnedURL(old);
+
+  if (IsURLPinned(url))
+    RemovePinnedURL(url);
+
+  Value* index = Value::CreateIntegerValue(pinned_index);
+  pinned_urls_->SetWithoutPathExpansion(GetURLString(url), index);
+
+  ResetThreadSafeCache();
+}
+
+bool TopSites::IsURLPinned(const GURL& url) {
+  int tmp;
+  return pinned_urls_->GetIntegerWithoutPathExpansion(GetURLString(url), &tmp);
+}
+
+void TopSites::RemovePinnedURL(const GURL& url) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
+  pinned_urls_->RemoveWithoutPathExpansion(GetURLString(url), NULL);
+
+  ResetThreadSafeCache();
+}
+
+bool TopSites::GetPinnedURLAtIndex(size_t index, GURL* url) {
+  for (DictionaryValue::key_iterator it = pinned_urls_->begin_keys();
+       it != pinned_urls_->end_keys(); ++it) {
+    int current_index;
+    if (pinned_urls_->GetIntegerWithoutPathExpansion(*it, &current_index)) {
+      if (static_cast<size_t>(current_index) == index) {
+        *url = GURL(*it);
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+void TopSites::Shutdown() {
+  profile_ = NULL;
+  // Cancel all requests so that the service doesn't callback to us after we've
+  // invoked Shutdown (this could happen if we have a pending request and
+  // Shutdown is invoked).
+  cancelable_consumer_.CancelAllRequests();
+  backend_->Shutdown();
+}
+
+// static
+void TopSites::DiffMostVisited(const MostVisitedURLList& old_list,
+                               const MostVisitedURLList& new_list,
+                               TopSitesDelta* delta) {
+  // Add all the old URLs for quick lookup. This maps URLs to the corresponding
+  // index in the input.
+  std::map<GURL, size_t> all_old_urls;
+  for (size_t i = 0; i < old_list.size(); i++)
+    all_old_urls[old_list[i].url] = i;
+
+  // Check all the URLs in the new set to see which ones are new or just moved.
+  // When we find a match in the old set, we'll reset its index to our special
+  // marker. This allows us to quickly identify the deleted ones in a later
+  // pass.
+  const size_t kAlreadyFoundMarker = static_cast<size_t>(-1);
+  for (size_t i = 0; i < new_list.size(); i++) {
+    std::map<GURL, size_t>::iterator found = all_old_urls.find(new_list[i].url);
+    if (found == all_old_urls.end()) {
+      MostVisitedURLWithRank added;
+      added.url = new_list[i];
+      added.rank = i;
+      delta->added.push_back(added);
+    } else {
+      if (found->second != i) {
+        MostVisitedURLWithRank moved;
+        moved.url = new_list[i];
+        moved.rank = i;
+        delta->moved.push_back(moved);
+      }
+      found->second = kAlreadyFoundMarker;
+    }
+  }
+
+  // Any member without the special marker in the all_old_urls list means that
+  // there wasn't a "new" URL that mapped to it, so it was deleted.
+  for (std::map<GURL, size_t>::const_iterator i = all_old_urls.begin();
+       i != all_old_urls.end(); ++i) {
+    if (i->second != kAlreadyFoundMarker)
+      delta->deleted.push_back(old_list[i->second]);
+  }
+}
+
+TopSites::~TopSites() {
+}
+
+bool TopSites::SetPageThumbnailNoDB(const GURL& url,
+                                    const RefCountedBytes* thumbnail_data,
+                                    const ThumbnailScore& score) {
+  // This should only be invoked when we know about the url.
+  DCHECK(cache_->IsKnownURL(url));
+
+  const MostVisitedURL& most_visited =
+      cache_->top_sites()[cache_->GetURLIndex(url)];
+  Images* image = cache_->GetImage(url);
 
   // When comparing the thumbnail scores, we need to take into account the
   // redirect hops, which are not generated when the thumbnail is because the
@@ -214,95 +460,136 @@ bool TopSites::SetPageThumbnailNoDB(const GURL& url,
   new_score_with_redirects.redirect_hops_from_dest =
       GetRedirectDistanceForURL(most_visited, url);
 
-  if (!ShouldReplaceThumbnailWith(image.thumbnail_score,
+  if (!ShouldReplaceThumbnailWith(image->thumbnail_score,
                                   new_score_with_redirects) &&
-      image.thumbnail.get())
+      image->thumbnail.get())
     return false;  // The one we already have is better.
 
-  // Take ownership of the thumbnail data.
-  image.thumbnail = const_cast<RefCountedBytes*>(thumbnail_data);
-  image.thumbnail_score = new_score_with_redirects;
+  image->thumbnail = const_cast<RefCountedBytes*>(thumbnail_data);
+  image->thumbnail_score = new_score_with_redirects;
 
+  ResetThreadSafeImageCache();
   return true;
 }
 
-void TopSites::GetMostVisitedURLs(CancelableRequestConsumer* consumer,
-                                  GetTopSitesCallback* callback) {
-  scoped_refptr<CancelableRequest<GetTopSitesCallback> > request(
-      new CancelableRequest<GetTopSitesCallback>(callback));
-  // This ensures cancelation of requests when either the consumer or the
-  // provider is deleted. Deletion of requests is also guaranteed.
-  AddRequest(request, consumer);
-  MostVisitedURLList filtered_urls;
-  {
-    AutoLock lock(lock_);
-    if (waiting_for_results_) {
-      // A request came in before we have any top sites.
-      // We have to keep track of the requests ourselves.
-      pending_callbacks_.insert(request);
+bool TopSites::SetPageThumbnailEncoded(const GURL& url,
+                                       const RefCountedBytes* thumbnail,
+                                       const ThumbnailScore& score) {
+  if (!SetPageThumbnailNoDB(url, thumbnail, score))
+    return false;
+
+  // Update the database.
+  if (!cache_->IsKnownURL(url))
+    return false;
+
+  size_t index = cache_->GetURLIndex(url);
+  const MostVisitedURL& most_visited = cache_->top_sites()[index];
+  backend_->SetPageThumbnail(most_visited,
+                             index,
+                             *(cache_->GetImage(most_visited.url)));
+  return true;
+}
+
+// static
+bool TopSites::EncodeBitmap(const SkBitmap& bitmap,
+                            scoped_refptr<RefCountedBytes>* bytes) {
+  *bytes = new RefCountedBytes();
+  SkAutoLockPixels bitmap_lock(bitmap);
+  std::vector<unsigned char> data;
+  if (!gfx::JPEGCodec::Encode(
+          reinterpret_cast<unsigned char*>(bitmap.getAddr32(0, 0)),
+          gfx::JPEGCodec::FORMAT_BGRA, bitmap.width(),
+          bitmap.height(),
+          static_cast<int>(bitmap.rowBytes()), 90,
+          &data)) {
+    return false;
+  }
+  // As we're going to cache this data, make sure the vector is only as big as
+  // it needs to be.
+  (*bytes)->data = data;
+  return true;
+}
+
+void TopSites::RemoveTemporaryThumbnailByURL(const GURL& url) {
+  for (TempImages::iterator i = temp_images_.begin(); i != temp_images_.end();
+       ++i) {
+    if (i->first == url) {
+      temp_images_.erase(i);
       return;
     }
-    if (request->canceled())
-      return;
-
-    ApplyBlacklistAndPinnedURLs(top_sites_, &filtered_urls);
   }
-  request->ForwardResult(GetTopSitesCallback::TupleType(filtered_urls));
 }
 
-bool TopSites::GetPageThumbnail(const GURL& url, RefCountedBytes** data) const {
-  AutoLock lock(lock_);
-  std::map<GURL, Images>::const_iterator found =
-      top_images_.find(GetCanonicalURL(url));
-  if (found == top_images_.end()) {
-    found = temp_thumbnails_map_.find(url);
-    if (found == temp_thumbnails_map_.end())
-      return false;  // No thumbnail for this URL.
+void TopSites::AddTemporaryThumbnail(const GURL& url,
+                                     const RefCountedBytes* thumbnail,
+                                     const ThumbnailScore& score) {
+  if (temp_images_.size() == kMaxTempTopImages)
+    temp_images_.erase(temp_images_.begin());
+
+  TempImage image;
+  image.first = url;
+  image.second.thumbnail = const_cast<RefCountedBytes*>(thumbnail);
+  image.second.thumbnail_score = score;
+  temp_images_.push_back(image);
+}
+
+void TopSites::StartQueryForMostVisited() {
+  if (!profile_)
+    return;
+
+  HistoryService* hs = profile_->GetHistoryService(Profile::EXPLICIT_ACCESS);
+  // |hs| may be null during unit tests.
+  if (hs) {
+    hs->QueryMostVisitedURLs(
+        num_results_to_request_from_history(),
+        kDaysOfHistory,
+        &cancelable_consumer_,
+        NewCallback(this, &TopSites::OnTopSitesAvailableFromHistory));
   }
+}
 
-  Images image = found->second;
-  *data = image.thumbnail.get();
-  return true;
+// static
+int TopSites::GetRedirectDistanceForURL(const MostVisitedURL& most_visited,
+                                        const GURL& url) {
+  for (size_t i = 0; i < most_visited.redirects.size(); i++) {
+    if (most_visited.redirects[i] == url)
+      return static_cast<int>(most_visited.redirects.size() - i - 1);
+  }
+  NOTREACHED() << "URL should always be found.";
+  return 0;
 }
 
-static int IndexOf(const MostVisitedURLList& urls, const GURL& url) {
-  for (size_t i = 0; i < urls.size(); i++) {
-    if (urls[i].url == url)
-      return i;
+// static
+MostVisitedURLList TopSites::GetPrepopulatePages() {
+  MostVisitedURLList urls;
+  urls.resize(arraysize(kPrepopulatePageIDs));
+  for (size_t i = 0; i < arraysize(kPrepopulatePageIDs); ++i) {
+    MostVisitedURL& url = urls[i];
+    url.url = GURL(l10n_util::GetStringUTF8(kPrepopulatePageIDs[i]));
+    url.redirects.push_back(url.url);
+    url.favicon_url = GURL(kPrepopulateFaviconURLs[i]);
+    url.title = l10n_util::GetStringUTF16(kPrepopulateTitleIDs[i]);
   }
-  return -1;
+  return urls;
 }
 
+// static
 bool TopSites::AddPrepopulatedPages(MostVisitedURLList* urls) {
-  // TODO(arv): This needs to get the data from some configurable place.
-  // http://crbug.com/17630
   bool added = false;
-  GURL welcome_url(l10n_util::GetStringUTF8(IDS_CHROME_WELCOME_URL));
-  if (urls->size() < kTopSitesNumber && IndexOf(*urls, welcome_url) == -1) {
-    MostVisitedURL url(
-        welcome_url,
-        GURL("chrome://theme/IDR_NEWTAB_CHROME_WELCOME_PAGE_FAVICON"),
-        l10n_util::GetStringUTF16(IDS_NEW_TAB_CHROME_WELCOME_PAGE_TITLE));
-    url.redirects.push_back(welcome_url);
-    urls->push_back(url);
-    added = true;
-  }
-
-  GURL themes_url(l10n_util::GetStringUTF8(IDS_THEMES_GALLERY_URL));
-  if (urls->size() < kTopSitesNumber && IndexOf(*urls, themes_url) == -1) {
-    MostVisitedURL url(
-        themes_url,
-        GURL("chrome://theme/IDR_NEWTAB_THEMES_GALLERY_FAVICON"),
-        l10n_util::GetStringUTF16(IDS_NEW_TAB_THEMES_GALLERY_PAGE_TITLE));
-    url.redirects.push_back(themes_url);
-    urls->push_back(url);
-    added = true;
+  MostVisitedURLList prepopulate_urls = GetPrepopulatePages();
+  for (size_t i = 0; i < prepopulate_urls.size(); ++i) {
+    if (urls->size() < kTopSitesNumber &&
+        IndexOf(*urls, prepopulate_urls[i].url) == -1) {
+      urls->push_back(prepopulate_urls[i]);
+      added = true;
+    }
   }
-
   return added;
 }
 
 void TopSites::MigratePinnedURLs() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+
   std::map<GURL, size_t> tmp_map;
   for (DictionaryValue::key_iterator it = pinned_urls_->begin_keys();
        it != pinned_urls_->end_keys(); ++it) {
@@ -327,7 +614,6 @@ void TopSites::MigratePinnedURLs() {
 
 void TopSites::ApplyBlacklistAndPinnedURLs(const MostVisitedURLList& urls,
                                            MostVisitedURLList* out) {
-  lock_.AssertAcquired();
   MostVisitedURLList urls_copy;
   for (size_t i = 0; i < urls.size(); i++) {
     if (!IsBlacklisted(urls[i].url))
@@ -375,521 +661,247 @@ void TopSites::ApplyBlacklistAndPinnedURLs(const MostVisitedURLList& urls,
 }
 
 std::string TopSites::GetURLString(const GURL& url) {
-  lock_.AssertAcquired();
-  return GetCanonicalURL(url).spec();
+  return cache_->GetCanonicalURL(url).spec();
 }
 
 std::string TopSites::GetURLHash(const GURL& url) {
-  lock_.AssertAcquired();
   // We don't use canonical URLs here to be able to blacklist only one of
   // the two 'duplicate' sites, e.g. 'gmail.com' and 'mail.google.com'.
   return MD5String(url.spec());
 }
 
-void TopSites::UpdateMostVisited(MostVisitedURLList most_visited) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
+base::TimeDelta TopSites::GetUpdateDelay() {
+  if (cache_->top_sites().size() <= arraysize(kPrepopulateTitleIDs))
+    return base::TimeDelta::FromSeconds(30);
 
-  std::vector<size_t> added;    // Indices into most_visited.
-  std::vector<size_t> deleted;  // Indices into top_sites_.
-  std::vector<size_t> moved;    // Indices into most_visited.
+  int64 range = kMaxUpdateIntervalMinutes - kMinUpdateIntervalMinutes;
+  int64 minutes = kMaxUpdateIntervalMinutes -
+      last_num_urls_changed_ * range / cache_->top_sites().size();
+  return base::TimeDelta::FromMinutes(minutes);
+}
 
-  DiffMostVisited(top_sites_, most_visited, &added, &deleted, &moved);
+// static
+void TopSites::ProcessPendingCallbacks(
+    const PendingCallbackSet& pending_callbacks,
+    const MostVisitedURLList& urls) {
+  PendingCallbackSet::const_iterator i;
+  for (i = pending_callbacks.begin();
+       i != pending_callbacks.end(); ++i) {
+    scoped_refptr<CancelableRequest<GetTopSitesCallback> > request = *i;
+    if (!request->canceled())
+      request->ForwardResult(GetTopSitesCallback::TupleType(urls));
+  }
+}
 
-  // #added == #deleted; #added + #moved = total.
-  last_num_urls_changed_ = added.size() + moved.size();
+void TopSites::Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details) {
+  if (!loaded_)
+    return;
 
-  {
-    AutoLock lock(lock_);
+  if (type == NotificationType::HISTORY_URLS_DELETED) {
+    Details<history::URLsDeletedDetails> deleted_details(details);
+    if (deleted_details->all_history) {
+      SetTopSites(MostVisitedURLList());
+      backend_->ResetDatabase();
+    } else {
+      std::set<size_t> indices_to_delete;  // Indices into top_sites_.
+      for (std::set<GURL>::iterator i = deleted_details->urls.begin();
+           i != deleted_details->urls.end(); ++i) {
+        if (cache_->IsKnownURL(*i))
+          indices_to_delete.insert(cache_->GetURLIndex(*i));
+      }
 
-    // Process the diff: delete from images and disk, add to disk.
-    // Delete all the thumbnails associated with URLs that were deleted.
-    for (size_t i = 0; i < deleted.size(); i++) {
-      const MostVisitedURL& deleted_url = top_sites_[deleted[i]];
-      std::map<GURL, Images>::iterator found =
-          top_images_.find(deleted_url.url);
-      if (found != top_images_.end())
-        top_images_.erase(found);
-    }
-  }
+      if (indices_to_delete.empty())
+        return;
 
-  // Write the updates to the DB.
-  if (db_.get()) {
-    for (size_t i = 0; i < deleted.size(); i++) {
-      const MostVisitedURL& deleted_url = top_sites_[deleted[i]];
-      if (db_.get())
-        db_->RemoveURL(deleted_url);
-    }
-    for (size_t i = 0; i < added.size(); i++) {
-      const MostVisitedURL& added_url = most_visited[added[i]];
-      db_->SetPageThumbnail(added_url, added[i], Images());
-    }
-    for (size_t i = 0; i < moved.size(); i++) {
-      const MostVisitedURL& moved_url = most_visited[moved[i]];
-      db_->UpdatePageRank(moved_url, moved[i]);
+      MostVisitedURLList new_top_sites(cache_->top_sites());
+      for (std::set<size_t>::reverse_iterator i = indices_to_delete.rbegin();
+           i != indices_to_delete.rend(); i++) {
+        size_t index = *i;
+        RemovePinnedURL(new_top_sites[index].url);
+        new_top_sites.erase(new_top_sites.begin() + index);
+      }
+      SetTopSites(new_top_sites);
     }
-  }
-
-  StoreMostVisited(&most_visited);
-  if (migration_in_progress_) {
-    // Copy all thumnbails from the history service.
-    for (size_t i = 0; i < top_sites_.size(); i++) {
-      GURL& url = top_sites_[i].url;
-      Images& img = top_images_[url];
-      if (!img.thumbnail.get() || !img.thumbnail->size()) {
-        StartQueryForThumbnail(i);
+    StartQueryForMostVisited();
+  } else if (type == NotificationType::NAV_ENTRY_COMMITTED) {
+    if (cache_->top_sites().size() < kTopSitesNumber) {
+      NavigationController::LoadCommittedDetails* load_details =
+          Details<NavigationController::LoadCommittedDetails>(details).ptr();
+      if (!load_details)
+        return;
+      const GURL& url = load_details->entry->url();
+      if (!cache_->IsKnownURL(url) && HistoryService::CanAddURL(url)) {
+        // To avoid slamming history we throttle requests when the url updates.
+        // To do otherwise negatively impacts perf tests.
+        RestartQueryForTopSitesTimer(GetUpdateDelay());
       }
     }
   }
-
-  // If we are not expecting any thumbnails, migration is done.
-  if (migration_in_progress_ && migration_pending_urls_.empty())
-    OnMigrationDone();
-
-  timer_.Stop();
-  timer_.Start(GetUpdateDelay(), this,
-               &TopSites::StartQueryForMostVisited);
 }
 
-void TopSites::OnMigrationDone() {
-  migration_in_progress_ = false;
-  if (!profile_)
-    return;
+void TopSites::SetTopSites(const MostVisitedURLList& new_top_sites) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  HistoryService* hs = profile_->GetHistoryService(Profile::EXPLICIT_ACCESS);
-  // |hs| may be null during unit tests.
-  if (!hs)
-    return;
-  hs->OnTopSitesReady();
-}
-
-void TopSites::AddTemporaryThumbnail(const GURL& url,
-                                     const RefCountedBytes* thumbnail,
-                                     const ThumbnailScore& score) {
-  Images& img = temp_thumbnails_map_[url];
-  img.thumbnail = const_cast<RefCountedBytes*>(thumbnail);
-  img.thumbnail_score = score;
-}
-
-void TopSites::StartQueryForThumbnail(size_t index) {
-  DCHECK(migration_in_progress_);
-  if (top_sites_[index].url.spec() ==
-      l10n_util::GetStringUTF8(IDS_CHROME_WELCOME_URL) ||
-      top_sites_[index].url.spec() ==
-      l10n_util::GetStringUTF8(IDS_THEMES_GALLERY_URL))
-    return;  // Don't need thumbnails for prepopulated URLs.
-
-  migration_pending_urls_.insert(top_sites_[index].url);
-
-  if (mock_history_service_) {
-    // Testing with a mockup.
-    // QueryMostVisitedURLs is not virtual, so we have to duplicate the code.
-    // This calls SetClientData.
-    mock_history_service_->GetPageThumbnail(
-        top_sites_[index].url,
-        &cancelable_consumer_,
-        NewCallback(this, &TopSites::OnThumbnailAvailable),
-        index);
-    return;
-  }
+  MostVisitedURLList top_sites(new_top_sites);
+  AddPrepopulatedPages(&top_sites);
 
-  if (!profile_)
-    return;
+  TopSitesDelta delta;
+  DiffMostVisited(cache_->top_sites(), top_sites, &delta);
+  if (!delta.deleted.empty() || !delta.added.empty() || !delta.moved.empty())
+    backend_->UpdateTopSites(delta);
 
-  HistoryService* hs = profile_->GetHistoryService(Profile::EXPLICIT_ACCESS);
-  // |hs| may be null during unit tests.
-  if (!hs)
-    return;
-  HistoryService::Handle handle =
-      hs->GetPageThumbnail(top_sites_[index].url,
-                           &cancelable_consumer_,
-                           NewCallback(this, &TopSites::OnThumbnailAvailable));
-  cancelable_consumer_.SetClientData(hs, handle, index);
-}
+  last_num_urls_changed_ = delta.added.size() + delta.moved.size();
 
-void TopSites::GenerateCanonicalURLs() {
-  lock_.AssertAcquired();
-  canonical_urls_.clear();
-  for (size_t i = 0; i < top_sites_.size(); i++) {
-    const MostVisitedURL& mv = top_sites_[i];
-    StoreRedirectChain(mv.redirects, i);
-  }
-}
+  // We always do the following steps (setting top sites in cache, and resetting
+  // thread safe cache ...) as this method is invoked during startup at which
+  // point the caches haven't been updated yet.
+  cache_->SetTopSites(top_sites);
 
-void TopSites::StoreMostVisited(MostVisitedURLList* most_visited) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
-  MostVisitedURLList filtered_urls;
-  PendingCallbackSet callbacks;
-  {
-    AutoLock lock(lock_);
-    top_sites_.clear();
-    // Take ownership of the most visited data.
-    top_sites_.swap(*most_visited);
-    waiting_for_results_ = false;
-
-    // Save the redirect information for quickly mapping to the canonical URLs.
-    GenerateCanonicalURLs();
-
-    for (size_t i = 0; i < top_sites_.size(); i++) {
-      const MostVisitedURL& mv = top_sites_[i];
-      std::map<GURL, Images>::iterator it = temp_thumbnails_map_.begin();
-      GURL canonical_url = GetCanonicalURL(mv.url);
-      for (; it != temp_thumbnails_map_.end(); it++) {
-        // Must map all temp URLs to canonical ones.
-        // temp_thumbnails_map_ contains non-canonical URLs, because
-        // when we add a temp thumbnail, redirect chain is not known.
-        // This is slow, but temp_thumbnails_map_ should have very few URLs.
-        if (canonical_url == GetCanonicalURL(it->first)) {
-          SetPageThumbnailEncoded(mv.url, it->second.thumbnail,
+  // See if we have any tmp thumbnails for the new sites.
+  if (!temp_images_.empty()) {
+    for (size_t i = 0; i < top_sites.size(); ++i) {
+      const MostVisitedURL& mv = top_sites[i];
+      GURL canonical_url = cache_->GetCanonicalURL(mv.url);
+      // At the time we get the thumbnail redirects aren't known, so we have to
+      // iterate through all the images.
+      for (TempImages::iterator it = temp_images_.begin();
+           it != temp_images_.end(); ++it) {
+        if (canonical_url == cache_->GetCanonicalURL(it->first)) {
+          SetPageThumbnailEncoded(mv.url,
+                                  it->second.thumbnail,
                                   it->second.thumbnail_score);
-          temp_thumbnails_map_.erase(it);
+          temp_images_.erase(it);
           break;
         }
       }
     }
-    if (top_sites_.size() >= kTopSitesNumber)
-      temp_thumbnails_map_.clear();
+  }
 
-    if (pending_callbacks_.empty())
-      return;
+  if (top_sites.size() >= kTopSitesNumber)
+    temp_images_.clear();
 
-    ApplyBlacklistAndPinnedURLs(top_sites_, &filtered_urls);
-    callbacks.swap(pending_callbacks_);
-  }  // lock_ is released.
-  // Process callbacks outside the lock - ForwardResults may cause
-  // thread switches.
-  ProcessPendingCallbacks(callbacks, filtered_urls);
-}
+  ResetThreadSafeCache();
+  ResetThreadSafeImageCache();
 
-void TopSites::StoreRedirectChain(const RedirectList& redirects,
-                                  size_t destination) {
-  lock_.AssertAcquired();
-  if (redirects.empty()) {
-    NOTREACHED();
-    return;
-  }
-
-  // Map all the redirected URLs to the destination.
-  for (size_t i = 0; i < redirects.size(); i++) {
-    // If this redirect is already known, don't replace it with a new one.
-    if (canonical_urls_.find(redirects[i]) == canonical_urls_.end())
-      canonical_urls_[redirects[i]] = destination;
-  }
+  // Restart the timer that queries history for top sites. This is done to
+  // ensure we stay in sync with history.
+  RestartQueryForTopSitesTimer(GetUpdateDelay());
 }
 
-GURL TopSites::GetCanonicalURL(const GURL& url) const {
-  lock_.AssertAcquired();
-  std::map<GURL, size_t>::const_iterator found = canonical_urls_.find(url);
-  if (found == canonical_urls_.end())
-    return url;  // Unknown URL - return unchanged.
-  return top_sites_[found->second].url;
-}
+int TopSites::num_results_to_request_from_history() const {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-// static
-int TopSites::GetRedirectDistanceForURL(const MostVisitedURL& most_visited,
-                                        const GURL& url) {
-  for (size_t i = 0; i < most_visited.redirects.size(); i++) {
-    if (most_visited.redirects[i] == url)
-      return static_cast<int>(most_visited.redirects.size() - i - 1);
-  }
-  NOTREACHED() << "URL should always be found.";
-  return 0;
+  return kTopSitesNumber + blacklist_->size();
 }
 
-// static
-void TopSites::DiffMostVisited(const MostVisitedURLList& old_list,
-                               const MostVisitedURLList& new_list,
-                               std::vector<size_t>* added_urls,
-                               std::vector<size_t>* deleted_urls,
-                               std::vector<size_t>* moved_urls) {
-  added_urls->clear();
-  deleted_urls->clear();
-  moved_urls->clear();
-
-  // Add all the old URLs for quick lookup. This maps URLs to the corresponding
-  // index in the input.
-  std::map<GURL, size_t> all_old_urls;
-  for (size_t i = 0; i < old_list.size(); i++)
-    all_old_urls[old_list[i].url] = i;
+void TopSites::MoveStateToLoaded() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  // Check all the URLs in the new set to see which ones are new or just moved.
-  // When we find a match in the old set, we'll reset its index to our special
-  // marker. This allows us to quickly identify the deleted ones in a later
-  // pass.
-  const size_t kAlreadyFoundMarker = static_cast<size_t>(-1);
-  for (size_t i = 0; i < new_list.size(); i++) {
-    std::map<GURL, size_t>::iterator found = all_old_urls.find(new_list[i].url);
-    if (found == all_old_urls.end()) {
-      added_urls->push_back(i);
-    } else {
-      if (found->second != i)
-        moved_urls->push_back(i);
-      found->second = kAlreadyFoundMarker;
-    }
-  }
+  MostVisitedURLList filtered_urls;
+  PendingCallbackSet pending_callbacks;
+  {
+    AutoLock lock(lock_);
 
-  // Any member without the special marker in the all_old_urls list means that
-  // there wasn't a "new" URL that mapped to it, so it was deleted.
-  for (std::map<GURL, size_t>::const_iterator i = all_old_urls.begin();
-       i != all_old_urls.end(); ++i) {
-    if (i->second != kAlreadyFoundMarker)
-      deleted_urls->push_back(i->second);
-  }
-}
+    if (loaded_)
+      return;  // Don't do anything if we're already loaded.
+    loaded_ = true;
 
-void TopSites::StartQueryForMostVisited() {
-  if (mock_history_service_) {
-    // Testing with a mockup.
-    // QueryMostVisitedURLs is not virtual, so we have to duplicate the code.
-    mock_history_service_->QueryMostVisitedURLs(
-        kTopSitesNumber + blacklist_->size(),
-        kDaysOfHistory,
-        &cancelable_consumer_,
-        NewCallback(this, &TopSites::OnTopSitesAvailable));
-  } else {
-    if (!profile_)
-      return;
-
-    HistoryService* hs = profile_->GetHistoryService(Profile::EXPLICIT_ACCESS);
-    // |hs| may be null during unit tests.
-    if (hs) {
-      hs->QueryMostVisitedURLs(
-          kTopSitesNumber + blacklist_->size(),
-          kDaysOfHistory,
-          &cancelable_consumer_,
-          NewCallback(this, &TopSites::OnTopSitesAvailable));
-    } else {
-      VLOG(1) << "History Service not available.";
+    // Now that we're loaded we can service the queued up callbacks. Copy them
+    // here and service them outside the lock.
+    if (!pending_callbacks_.empty()) {
+      filtered_urls = thread_safe_cache_->top_sites();
+      pending_callbacks.swap(pending_callbacks_);
     }
   }
-}
 
-void TopSites::StartMigration() {
-  VLOG(1) << "Starting migration to TopSites.";
-  migration_in_progress_ = true;
-  StartQueryForMostVisited();
-  MigratePinnedURLs();
-}
+  ProcessPendingCallbacks(pending_callbacks, filtered_urls);
 
-bool TopSites::HasBlacklistedItems() const {
-  AutoLock lock(lock_);
-  return !blacklist_->empty();
+  NotificationService::current()->Notify(NotificationType::TOP_SITES_LOADED,
+                                         Source<Profile>(profile_),
+                                         Details<TopSites>(this));
 }
 
-void TopSites::AddBlacklistedURL(const GURL& url) {
+void TopSites::ResetThreadSafeCache() {
   AutoLock lock(lock_);
-  RemovePinnedURLLocked(url);
-  Value* dummy = Value::CreateNullValue();
-  blacklist_->SetWithoutPathExpansion(GetURLHash(url), dummy);
+  MostVisitedURLList cached;
+  ApplyBlacklistAndPinnedURLs(cache_->top_sites(), &cached);
+  thread_safe_cache_->SetTopSites(cached);
 }
 
-bool TopSites::IsBlacklisted(const GURL& url) {
-  lock_.AssertAcquired();
-  bool result = blacklist_->HasKey(GetURLHash(url));
-  return result;
-}
-
-void TopSites::RemoveBlacklistedURL(const GURL& url) {
+void TopSites::ResetThreadSafeImageCache() {
   AutoLock lock(lock_);
-  blacklist_->RemoveWithoutPathExpansion(GetURLHash(url), NULL);
-}
-
-void TopSites::ClearBlacklistedURLs() {
-  blacklist_->Clear();
+  thread_safe_cache_->SetThumbnails(cache_->images());
+  thread_safe_cache_->RemoveUnreferencedThumbnails();
 }
 
-void TopSites::AddPinnedURL(const GURL& url, size_t pinned_index) {
-  GURL old;
-  if (GetPinnedURLAtIndex(pinned_index, &old)) {
-    RemovePinnedURL(old);
-  }
-
-  if (IsURLPinned(url)) {
-    RemovePinnedURL(url);
+void TopSites::RestartQueryForTopSitesTimer(base::TimeDelta delta) {
+  if (timer_.IsRunning() && ((timer_start_time_ + timer_.GetCurrentDelay()) <
+                             (base::TimeTicks::Now() + delta))) {
+    return;
   }
 
-  Value* index = Value::CreateIntegerValue(pinned_index);
-  AutoLock lock(lock_);
-  pinned_urls_->SetWithoutPathExpansion(GetURLString(url), index);
-}
-
-void TopSites::RemovePinnedURL(const GURL& url) {
-  AutoLock lock(lock_);
-  RemovePinnedURLLocked(url);
-}
-
-void TopSites::RemovePinnedURLLocked(const GURL& url) {
-  lock_.AssertAcquired();
-  pinned_urls_->RemoveWithoutPathExpansion(GetURLString(url), NULL);
+  timer_start_time_ = base::TimeTicks::Now();
+  timer_.Stop();
+  timer_.Start(delta, this, &TopSites::StartQueryForMostVisited);
 }
 
-bool TopSites::IsURLPinned(const GURL& url) {
-  AutoLock lock(lock_);
-  int tmp;
-  bool result = pinned_urls_->GetIntegerWithoutPathExpansion(
-      GetURLString(url), &tmp);
-  return result;
-}
+void TopSites::OnHistoryMigrationWrittenToDisk(TopSitesBackend::Handle handle) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-bool TopSites::GetPinnedURLAtIndex(size_t index, GURL* url) {
-  for (DictionaryValue::key_iterator it = pinned_urls_->begin_keys();
-       it != pinned_urls_->end_keys(); ++it) {
-    int current_index;
-    if (pinned_urls_->GetIntegerWithoutPathExpansion(*it, &current_index)) {
-      if (static_cast<size_t>(current_index) == index) {
-        *url = GURL(*it);
-        return true;
-      }
-    }
-  }
-  return false;
-}
-
-// static
-void TopSites::DeleteTopSites(scoped_refptr<TopSites>& ptr) {
-  if (!ptr.get() || !MessageLoop::current())
+  if (!profile_)
     return;
-  if (BrowserThread::IsWellKnownThread(BrowserThread::UI)) {
-    ptr = NULL;
-  } else {
-    // Need to roll our own UI thread.
-    BrowserThread ui_loop(BrowserThread::UI, MessageLoop::current());
-    ptr = NULL;
-    MessageLoop::current()->RunAllPending();
-  }
-}
-
-void TopSites::ClearProfile() {
-  profile_ = NULL;
-}
-
-base::TimeDelta TopSites::GetUpdateDelay() {
-  AutoLock lock(lock_);
-  if (top_sites_.size() == 0)
-    return base::TimeDelta::FromSeconds(30);
 
-  int64 range = kMaxUpdateIntervalMinutes - kMinUpdateIntervalMinutes;
-  int64 minutes = kMaxUpdateIntervalMinutes -
-      last_num_urls_changed_ * range / top_sites_.size();
-  return base::TimeDelta::FromMinutes(minutes);
+  HistoryService* history =
+      profile_->GetHistoryService(Profile::EXPLICIT_ACCESS);
+  if (history)
+    history->OnTopSitesReady();
 }
 
-void TopSites::OnTopSitesAvailable(
+void TopSites::OnGotMostVisitedThumbnails(
     CancelableRequestProvider::Handle handle,
-    MostVisitedURLList pages) {
-  AddPrepopulatedPages(&pages);
-  BrowserThread::PostTask(BrowserThread::DB, FROM_HERE, NewRunnableMethod(
-      this, &TopSites::UpdateMostVisited, pages));
-}
+    scoped_refptr<MostVisitedThumbnails> data,
+    bool may_need_history_migration) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK_EQ(top_sites_state_, TOP_SITES_LOADING);
 
-// static
-void TopSites::ProcessPendingCallbacks(PendingCallbackSet pending_callbacks,
-                                       const MostVisitedURLList& urls) {
-  PendingCallbackSet::iterator i;
-  for (i = pending_callbacks.begin();
-       i != pending_callbacks.end(); ++i) {
-    scoped_refptr<CancelableRequest<GetTopSitesCallback> > request = *i;
-    if (!request->canceled())
-      request->ForwardResult(GetTopSitesCallback::TupleType(urls));
-  }
-  pending_callbacks.clear();
-}
+  if (!may_need_history_migration) {
+    top_sites_state_ = TOP_SITES_LOADED;
 
-void TopSites::OnThumbnailAvailable(CancelableRequestProvider::Handle handle,
-                                    scoped_refptr<RefCountedBytes> thumbnail) {
-  size_t index;
-  if (mock_history_service_) {
-    index = handle;
-  } else {
-    if (!profile_)
-      return;
+    // Set the top sites directly in the cache so that SetTopSites diffs
+    // correctly.
+    cache_->SetTopSites(data->most_visited);
+    SetTopSites(data->most_visited);
+    cache_->SetThumbnails(data->url_to_images_map);
 
-    HistoryService* hs = profile_ ->GetHistoryService(Profile::EXPLICIT_ACCESS);
-    if (!hs)
-      return;
-    index = cancelable_consumer_.GetClientData(hs, handle);
-  }
-  DCHECK(static_cast<size_t>(index) < top_sites_.size());
+    ResetThreadSafeImageCache();
 
-  if (migration_in_progress_)
-    migration_pending_urls_.erase(top_sites_[index].url);
+    MoveStateToLoaded();
 
-  if (thumbnail.get() && thumbnail->size()) {
-    const MostVisitedURL& url = top_sites_[index];
-    AutoLock lock(lock_);
-    SetPageThumbnailEncoded(url.url, thumbnail, ThumbnailScore());
-  }
-
-  if (migration_in_progress_ && migration_pending_urls_.empty() &&
-      !mock_history_service_)
-    OnMigrationDone();
-}
-
-void TopSites::SetMockHistoryService(MockHistoryService* mhs) {
-  mock_history_service_ = mhs;
-}
-
-void TopSites::Observe(NotificationType type,
-                       const NotificationSource& source,
-                       const NotificationDetails& details) {
-  AutoLock lock(lock_);
-  if (type == NotificationType::HISTORY_URLS_DELETED) {
-    Details<history::URLsDeletedDetails> deleted_details(details);
-    if (deleted_details->all_history) {
-      top_sites_.clear();
-      BrowserThread::PostTask(
-          BrowserThread::DB, FROM_HERE,
-          NewRunnableMethod(this, &TopSites::ResetDatabase));
+    // Start a timer that refreshes top sites from history.
+    RestartQueryForTopSitesTimer(
+        base::TimeDelta::FromSeconds(kUpdateIntervalSecs));
+  } else {
+    // The top sites file didn't exist or is the wrong version. We need to wait
+    // for history to finish loading to know if we really needed to migrate.
+    if (history_state_ == HISTORY_LOADED) {
+      top_sites_state_ = TOP_SITES_LOADED;
+      SetTopSites(MostVisitedURLList());
+      MoveStateToLoaded();
     } else {
-      std::set<size_t> indices_to_delete;  // Indices into top_sites_.
-      std::set<GURL>::iterator it;
-      for (it = deleted_details->urls.begin();
-           it != deleted_details->urls.end(); ++it) {
-        std::map<GURL,size_t>::const_iterator found = canonical_urls_.find(*it);
-        if (found != canonical_urls_.end())
-          indices_to_delete.insert(found->second);
-      }
-
-      for (std::set<size_t>::reverse_iterator i = indices_to_delete.rbegin();
-           i != indices_to_delete.rend(); i++) {
-        size_t index = *i;
-        RemovePinnedURLLocked(top_sites_[index].url);
-        top_sites_.erase(top_sites_.begin() + index);
-      }
-    }
-    // Canonical URLs are not valid any more.
-    GenerateCanonicalURLs();
-    StartQueryForMostVisited();
-  } else if (type == NotificationType::NAV_ENTRY_COMMITTED) {
-    if (top_sites_.size() < kTopSitesNumber) {
-      NavigationController::LoadCommittedDetails* load_details =
-          Details<NavigationController::LoadCommittedDetails>(details).ptr();
-      if (!load_details)
-        return;
-      GURL url = load_details->entry->url();
-      if (canonical_urls_.find(url) == canonical_urls_.end() &&
-          HistoryService::CanAddURL(url)) {
-        // Add this page to the known pages in case the thumbnail comes
-        // in before we get the results.
-        MostVisitedURL mv;
-        mv.url = url;
-        mv.redirects.push_back(url);
-        top_sites_.push_back(mv);
-        size_t index = top_sites_.size() - 1;
-        StoreRedirectChain(top_sites_[index].redirects, index);
-      }
-      StartQueryForMostVisited();
+      top_sites_state_ = TOP_SITES_LOADED_WAITING_FOR_HISTORY;
+      // Ask for history just in case it hasn't been loaded yet. When history
+      // finishes loading we'll do migration and/or move to loaded.
+      profile_->GetHistoryService(Profile::EXPLICIT_ACCESS);
     }
   }
 }
 
-void TopSites::ResetDatabase() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
-  db_.reset(new TopSitesDatabaseImpl());
-  file_util::Delete(db_path_, false);
-  if (!db_->Init(db_path_)) {
-    NOTREACHED() << "Failed to initialize database.";
-    return;
-  }
+void TopSites::OnTopSitesAvailableFromHistory(
+    CancelableRequestProvider::Handle handle,
+    MostVisitedURLList pages) {
+  SetTopSites(pages);
 }
 
 }  // namespace history
diff --git a/chrome/browser/history/top_sites.h b/chrome/browser/history/top_sites.h
index f080c05..bd406f1 100644
--- a/chrome/browser/history/top_sites.h
+++ b/chrome/browser/history/top_sites.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -6,14 +6,14 @@
 #define CHROME_BROWSER_HISTORY_TOP_SITES_H_
 #pragma once
 
-#include <map>
+#include <list>
 #include <set>
 #include <string>
-#include <vector>
 
 #include "base/basictypes.h"
 #include "base/gtest_prod_util.h"
 #include "base/lock.h"
+#include "base/time.h"
 #include "base/timer.h"
 #include "base/ref_counted.h"
 #include "base/ref_counted_memory.h"
@@ -27,30 +27,26 @@
 #include "googleurl/src/gurl.h"
 
 class DictionaryValue;
+class FilePath;
 class SkBitmap;
 class Profile;
 
 namespace history {
 
+class TopSitesCache;
 class TopSitesBackend;
-class TopSitesDatabase;
 class TopSitesTest;
 
-typedef std::vector<MostVisitedURL> MostVisitedURLList;
-
 // Stores the data for the top "most visited" sites. This includes a cache of
 // the most visited data from history, as well as the corresponding thumbnails
 // of those sites.
 //
-// This class IS threadsafe. It is designed to be used from the UI thread of
-// the browser (where history requests must be kicked off and received from)
-// and from the I/O thread (where new tab page requests come in). Handling the
-// new tab page requests on the I/O thread without proxying to the UI thread is
-// a nontrivial performance win, especially when the browser is starting and
-// the UI thread is busy.
-class TopSites :
-      public base::RefCountedThreadSafe<TopSites,
-                                        BrowserThread::DeleteOnUIThread>,
+// This class allows requests for most visited urls and thumbnails on any
+// thread. All other methods must be invoked on the UI thread. All mutations
+// to internal state happen on the UI thread and are scheduled to update the
+// db using TopSitesBackend.
+class TopSites
+    : public base::RefCountedThreadSafe<TopSites>,
       public NotificationObserver,
       public CancelableRequestProvider {
  public:
@@ -59,21 +55,6 @@ class TopSites :
   // Returns whether top sites is enabled.
   static bool IsEnabled();
 
-  class MockHistoryService {
-    // A mockup of a HistoryService used for testing TopSites.
-   public:
-    virtual HistoryService::Handle QueryMostVisitedURLs(
-        int result_count, int days_back,
-        CancelableRequestConsumerBase* consumer,
-        HistoryService::QueryMostVisitedURLsCallback* callback) = 0;
-    virtual ~MockHistoryService() {}
-    virtual void GetPageThumbnail(
-        const GURL& page_url,
-        CancelableRequestConsumerTSimple<size_t>* consumer,
-        HistoryService::ThumbnailDataCallback* callback,
-        size_t index) = 0;
-  };
-
   // Initializes TopSites.
   void Init(const FilePath& db_name);
 
@@ -85,23 +66,33 @@ class TopSites :
                         const ThumbnailScore& score);
 
   // Callback for GetMostVisitedURLs.
-  typedef Callback1<MostVisitedURLList>::Type GetTopSitesCallback;
+  typedef Callback1<const MostVisitedURLList&>::Type GetTopSitesCallback;
   typedef std::set<scoped_refptr<CancelableRequest<GetTopSitesCallback> > >
       PendingCallbackSet;
 
   // Returns a list of most visited URLs via a callback.
+  // This may be invoked on any thread.
   // NOTE: the callback may be called immediately if we have the data cached.
   void GetMostVisitedURLs(CancelableRequestConsumer* consumer,
                           GetTopSitesCallback* callback);
 
   // Get a thumbnail for a given page. Returns true iff we have the thumbnail.
-  bool GetPageThumbnail(const GURL& url, RefCountedBytes** data) const;
+  // This may be invoked on any thread.
+  // As this method may be invoked on any thread the ref count needs to be
+  // upped before this method returns, so this takes a scoped_refptr*.
+  bool GetPageThumbnail(const GURL& url,
+                        scoped_refptr<RefCountedBytes>* bytes);
+
+  // Invoked from History if migration is needed. If this is invoked it will
+  // be before HistoryLoaded is invoked.
+  void MigrateFromHistory();
 
-  // For testing with a HistoryService mock.
-  void SetMockHistoryService(MockHistoryService* mhs);
+  // Invoked with data from migrating thumbnails out of history.
+  void FinishHistoryMigration(const ThumbnailMigration& data);
 
-  // Start reading thumbnails from the ThumbnailDatabase.
-  void StartMigration();
+  // Invoked from history when it finishes loading. If MigrateFromHistory was
+  // not invoked at this point then we load from the top sites service.
+  void HistoryLoaded();
 
   // Blacklisted URLs
 
@@ -114,6 +105,9 @@ class TopSites :
   // Removes a URL from the blacklist.
   void RemoveBlacklistedURL(const GURL& url);
 
+  // Returns true if the URL is blacklisted.
+  bool IsBlacklisted(const GURL& url);
+
   // Clear the blacklist.
   void ClearBlacklistedURLs();
 
@@ -132,34 +126,53 @@ class TopSites :
   // is a URL pinned at |index|.
   bool GetPinnedURLAtIndex(size_t index, GURL* out);
 
-  // TopSites must be deleted on a UI thread. This happens
-  // automatically in a real browser, but in unit_tests we don't have
-  // a real UI thread. Use this function to delete a TopSites object.
-  static void DeleteTopSites(scoped_refptr<TopSites>& ptr);
+  // Shuts down top sites.
+  void Shutdown();
 
-  // Sets the profile pointer to NULL. This is for the case where
-  // TopSites outlives the profile, since TopSites is refcounted.
-  void ClearProfile();
+  // Generates the diff of things that happened between "old" and "new."
+  //
+  // The URLs that are in "new" but not "old" will be have their index into
+  // "new" put in |added_urls|. The URLs that are in "old" but not "new" will
+  // have their index into "old" put into |deleted_urls|.
+  //
+  // URLs appearing in both old and new lists but having different indices will
+  // have their index into "new" be put into |moved_urls|.
+  static void DiffMostVisited(const MostVisitedURLList& old_list,
+                              const MostVisitedURLList& new_list,
+                              TopSitesDelta* delta);
 
  private:
-  friend struct BrowserThread::DeleteOnThread<BrowserThread::UI>;
-  friend class DeleteTask<TopSites>;
+  friend class base::RefCountedThreadSafe<TopSites>;
   friend class TopSitesTest;
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, GetMostVisited);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, RealDatabase);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, MockDatabase);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, DeleteNotifications);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, PinnedURLsDeleted);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, GetUpdateDelay);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, Migration);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, QueueingRequestsForTopSites);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, CancelingRequestsForTopSites);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, AddTemporaryThumbnail);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, Blacklisting);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, PinnedURLs);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, BlacklistingAndPinnedURLs);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, AddPrepopulatedPages);
-  FRIEND_TEST_ALL_PREFIXES(TopSitesTest, GetPageThumbnail);
+
+  typedef std::pair<GURL, Images> TempImage;
+  typedef std::list<TempImage> TempImages;
+
+  // Enumeration of the possible states history can be in.
+  enum HistoryLoadState {
+    // We're waiting for history to finish loading.
+    HISTORY_LOADING,
+
+    // History finished loading and we need to migrate top sites out of history.
+    HISTORY_MIGRATING,
+
+    // History is loaded.
+    HISTORY_LOADED
+  };
+
+  // Enumeration of possible states the top sites backend can be in.
+  enum TopSitesLoadState {
+    // We're waiting for the backend to finish loading.
+    TOP_SITES_LOADING,
+
+    // The backend finished loading, but we may need to migrate. This is true if
+    // the top sites db didn't exist, or if the db existed but is from an old
+    // version.
+    TOP_SITES_LOADED_WAITING_FOR_HISTORY,
+
+    // Top sites is loaded.
+    TOP_SITES_LOADED
+  };
 
   ~TopSites();
 
@@ -176,44 +189,22 @@ class TopSites :
                                const RefCountedBytes* thumbnail,
                                const ThumbnailScore& score);
 
-  // Query history service for the list of available thumbnails.
-  void StartQueryForMostVisited();
-
-  // Query history service for the thumbnail for a given url. |index|
-  // is the index into top_sites_.
-  void StartQueryForThumbnail(size_t index);
-
-  // Called when history service returns a list of top URLs.
-  void OnTopSitesAvailable(CancelableRequestProvider::Handle handle,
-                           MostVisitedURLList data);
-
-  // Returns a list of urls to each pending callback.
-  static void ProcessPendingCallbacks(PendingCallbackSet pending_callbacks,
-                                      const MostVisitedURLList& urls);
-
-  // Called when history service returns a thumbnail.
-  void OnThumbnailAvailable(CancelableRequestProvider::Handle handle,
-                            scoped_refptr<RefCountedBytes> thumbnail);
+  // Encodes the bitmap to bytes for storage to the db. Returns true if the
+  // bitmap was successfully encoded.
+  static bool EncodeBitmap(const SkBitmap& bitmap,
+                           scoped_refptr<RefCountedBytes>* bytes);
 
-  // Sets canonical_urls_ from top_sites_.
-  void GenerateCanonicalURLs();
+  // Removes the cached thumbnail for url. Does nothing if |url| if not cached
+  // in |temp_images_|.
+  void RemoveTemporaryThumbnailByURL(const GURL& url);
 
-  // Saves the set of the top URLs visited by this user. The 0th item is the
-  // most popular.
-  // DANGER! This will clear all data from the input argument.
-  void StoreMostVisited(MostVisitedURLList* most_visited);
-
-  // Saves the given set of redirects. The redirects are in order of the
-  // given vector, so [0] -> [1] -> [2].
-  void StoreRedirectChain(const RedirectList& redirects,
-                          size_t destination);
+  // Add a thumbnail for an unknown url. See temp_thumbnails_map_.
+  void AddTemporaryThumbnail(const GURL& url,
+                             const RefCountedBytes* thumbnail,
+                             const ThumbnailScore& score);
 
-  // Each item in the most visited view can redirect elsewhere. This returns
-  // the canonical URL one identifying the site if the given URL does appear
-  // in the "top sites" list.
-  //
-  // If the given URL is not in the top sites, this will return an empty GURL.
-  GURL GetCanonicalURL(const GURL& url) const;
+  // Query history service for the list of available thumbnails.
+  void StartQueryForMostVisited();
 
   // Finds the given URL in the redirect chain for the given TopSite, and
   // returns the distance from the destination in hops that the given URL is.
@@ -221,131 +212,114 @@ class TopSites :
   static int GetRedirectDistanceForURL(const MostVisitedURL& most_visited,
                                        const GURL& url);
 
-  // Generates the diff of things that happened between "old" and "new."
-  //
-  // The URLs that are in "new" but not "old" will be have their index into
-  // "new" put in |added_urls|. The URLs that are in "old" but not "new" will
-  // have their index into "old" put into |deleted_urls|.
-  //
-  // URLs appearing in both old and new lists but having different indices will
-  // have their index into "new" be put into |moved_urls|.
-  static void DiffMostVisited(const MostVisitedURLList& old_list,
-                              const MostVisitedURLList& new_list,
-                              std::vector<size_t>* added_urls,
-                              std::vector<size_t>* deleted_urls,
-                              std::vector<size_t>* moved_urls);
+  // Returns the set of prepopulate pages.
+  static MostVisitedURLList GetPrepopulatePages();
 
-  // Implementation of NotificationObserver.
-  virtual void Observe(NotificationType type,
-                       const NotificationSource& source,
-                       const NotificationDetails& details);
+  // Add prepopulated pages: 'welcome to Chrome' and themes gallery to |urls|.
+  // Returns true if any pages were added.
+  static bool AddPrepopulatedPages(MostVisitedURLList* urls);
 
-  // Returns true if the URL is blacklisted.
-  bool IsBlacklisted(const GURL& url);
+  // Convert pinned_urls_ dictionary to the new format. Use URLs as
+  // dictionary keys.
+  void MigratePinnedURLs();
+
+  // Takes |urls|, produces it's copy in |out| after removing
+  // blacklisted URLs and reordering pinned URLs.
+  void ApplyBlacklistAndPinnedURLs(const MostVisitedURLList& urls,
+                                   MostVisitedURLList* out);
 
-  // A variant of RemovePinnedURL that must be called within a lock.
-  void RemovePinnedURLLocked(const GURL& url);
+  // Converts a url into a canonical string representation.
+  std::string GetURLString(const GURL& url);
+
+  // Returns an MD5 hash of the URL. Hashing is required for blacklisted URLs.
+  std::string GetURLHash(const GURL& url);
 
   // Returns the delay until the next update of history is needed.
   // Uses num_urls_changed
   base::TimeDelta GetUpdateDelay();
 
-  // The following methods must be run on the DB thread since they
-  // access the database.
+  // Executes all of the callbacks in |pending_callbacks|. This is used after
+  // we finish loading if any requests came in before we loaded.
+  static void ProcessPendingCallbacks(
+      const PendingCallbackSet& pending_callbacks,
+      const MostVisitedURLList& urls);
 
-  // Reads the database from disk. Called on startup to get the last
-  // known top sites.
-  void ReadDatabase();
+  // Implementation of NotificationObserver.
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
 
-  // Write a thumbnail to database.
-  void WriteThumbnailToDB(const MostVisitedURL& url,
-                          int url_rank,
-                          const Images& thumbnail);
+  // Resets top_sites_ and updates the db (in the background). All mutations to
+  // top_sites_ *must* go through this.
+  void SetTopSites(const MostVisitedURLList& new_top_sites);
 
-  // Updates the top sites list and writes the difference to disk.
-  void UpdateMostVisited(MostVisitedURLList most_visited);
+  // Returns the number of most visted results to request from history. This
+  // changes depending upon how many urls have been blacklisted.
+  int num_results_to_request_from_history() const;
 
-  // Deletes the database file, then reinitializes the database.
-  void ResetDatabase();
+  // Invoked when transitioning to LOADED. Notifies any queued up callbacks.
+  void MoveStateToLoaded();
 
-  // Called after TopSites completes migration.
-  void OnMigrationDone();
+  void ResetThreadSafeCache();
 
-  // Add a thumbnail for an unknown url. See temp_thumbnails_map_.
-  void AddTemporaryThumbnail(const GURL& url,
-                             const RefCountedBytes* thumbnail,
-                             const ThumbnailScore& score);
+  void ResetThreadSafeImageCache();
 
-  // Add prepopulated pages: 'welcome to Chrome' and themes gallery.
-  // Returns true if any pages were added.
-  bool AddPrepopulatedPages(MostVisitedURLList* urls);
+  // Stops and starts timer with a delay of |delta|.
+  void RestartQueryForTopSitesTimer(base::TimeDelta delta);
 
-  // Convert pinned_urls_ dictionary to the new format. Use URLs as
-  // dictionary keys.
-  void MigratePinnedURLs();
+  // Callback after TopSitesBackend has finished migration. This tells history
+  // to finish it's side of migration (nuking thumbnails on disk).
+  void OnHistoryMigrationWrittenToDisk(
+      CancelableRequestProvider::Handle handle);
 
-  // Takes |urls|, produces it's copy in |out| after removing
-  // blacklisted URLs and reordering pinned URLs.
-  void ApplyBlacklistAndPinnedURLs(const MostVisitedURLList& urls,
-                                   MostVisitedURLList* out);
+  // Callback from TopSites with the top sites/thumbnails.
+  void OnGotMostVisitedThumbnails(CancelableRequestProvider::Handle handle,
+                                  scoped_refptr<MostVisitedThumbnails> data,
+                                  bool may_need_history_migration);
 
-  // Converts a url into a canonical string representation.
-  std::string GetURLString(const GURL& url);
+  // Called when history service returns a list of top URLs.
+  void OnTopSitesAvailableFromHistory(CancelableRequestProvider::Handle handle,
+                                      MostVisitedURLList data);
 
-  // Returns an MD5 hash of the URL. Hashing is required for blacklisted URLs.
-  std::string GetURLHash(const GURL& url);
+  scoped_refptr<TopSitesBackend> backend_;
 
-  Profile* profile_;
-  // A mockup to use for testing. If NULL, use the real HistoryService
-  // from the profile_. See SetMockHistoryService.
-  MockHistoryService* mock_history_service_;
-  CancelableRequestConsumerTSimple<size_t> cancelable_consumer_;
-  mutable Lock lock_;
+  // The top sites data.
+  scoped_ptr<TopSitesCache> cache_;
 
-  // The cached version of the top sites. The 0th item in this vector is the
-  // #1 site.
-  MostVisitedURLList top_sites_;
+  // Copy of the top sites data that may be accessed on any thread (assuming
+  // you hold |lock_|). The data in |thread_safe_cache_| has blacklisted and
+  // pinned urls applied (|cache_| does not).
+  scoped_ptr<TopSitesCache> thread_safe_cache_;
 
-  // The images corresponding to the top_sites. This is indexed by the URL of
-  // the top site, so this doesn't have to be shuffled around when the ordering
-  // changes of the top sites. Some top_sites_ entries may not have images.
-  std::map<GURL, Images> top_images_;
+  Profile* profile_;
+
+  // Lock used to access |thread_safe_cache_|.
+  mutable Lock lock_;
 
-  // Generated from the redirects to and from the most visited pages, this
-  // maps the redirects to the index into top_sites_ that contains it.
-  std::map<GURL, size_t> canonical_urls_;
+  CancelableRequestConsumer cancelable_consumer_;
 
-  // Timer for updating TopSites data.
+  // Timer that asks history for the top sites. This is used to make sure our
+  // data stays in sync with history.
   base::OneShotTimer<TopSites> timer_;
 
-  scoped_ptr<TopSitesDatabase> db_;
-  FilePath db_path_;
+  // The time we started |timer_| at. Only valid if |timer_| is running.
+  base::TimeTicks timer_start_time_;
 
   NotificationRegistrar registrar_;
 
   // The number of URLs changed on the last update.
   size_t last_num_urls_changed_;
 
-  // Are we in the middle of migration from ThumbnailsDatabase to
-  // TopSites?
-  bool migration_in_progress_;
-
-  // URLs for which we are expecting thumbnails.
-  std::set<GURL> migration_pending_urls_;
-
   // The map of requests for the top sites list. Can only be
   // non-empty at startup. After we read the top sites from the DB, we'll
   // always have a cached list.
   PendingCallbackSet pending_callbacks_;
 
-  // Are we waiting for the top sites from HistoryService?
-  bool waiting_for_results_;
-
   // Stores thumbnails for unknown pages. When SetPageThumbnail is
   // called, if we don't know about that URL yet and we don't have
   // enough Top Sites (new profile), we store it until the next
-  // UpdateMostVisitedURLs call.
-  std::map<GURL, Images> temp_thumbnails_map_;
+  // SetTopSites call.
+  TempImages temp_images_;
 
   // Blacklisted and pinned URLs are stored in Preferences.
 
@@ -356,12 +330,20 @@ class TopSites :
   // PrefService.
   DictionaryValue* blacklist_;
 
-  // This is a dictionary for the pinned URLs for the the most visited
-  // part of the new tab page. Key is the URL, value is
-  // index where it is pinned at (may be the same as key). This is
-  // owned by the PrefService.
+  // This is a dictionary for the pinned URLs for the the most visited part of
+  // the new tab page. Key is the URL, value is index where it is pinned at (may
+  // be the same as key). This is owned by the PrefService.
   DictionaryValue* pinned_urls_;
 
+  // See description above HistoryLoadState.
+  HistoryLoadState history_state_;
+
+  // See description above TopSitesLoadState.
+  TopSitesLoadState top_sites_state_;
+
+  // Are we loaded?
+  bool loaded_;
+
   DISALLOW_COPY_AND_ASSIGN(TopSites);
 };
 
diff --git a/chrome/browser/history/top_sites_backend.cc b/chrome/browser/history/top_sites_backend.cc
new file mode 100644
index 0000000..eb27a5e
--- /dev/null
+++ b/chrome/browser/history/top_sites_backend.cc
@@ -0,0 +1,153 @@
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/history/top_sites_backend.h"
+
+#include "base/file_path.h"
+#include "base/file_util.h"
+#include "chrome/browser/browser_thread.h"
+#include "chrome/browser/history/top_sites_database.h"
+
+namespace history {
+
+TopSitesBackend::TopSitesBackend()
+    : db_(new TopSitesDatabase()) {
+}
+
+void TopSitesBackend::Init(const FilePath& path) {
+  db_path_ = path;
+  BrowserThread::PostTask(
+      BrowserThread::DB, FROM_HERE, NewRunnableMethod(
+          this, &TopSitesBackend::InitDBOnDBThread, path));
+}
+
+void TopSitesBackend::Shutdown() {
+  BrowserThread::PostTask(
+      BrowserThread::DB, FROM_HERE, NewRunnableMethod(
+          this, &TopSitesBackend::ShutdownDBOnDBThread));
+}
+
+TopSitesBackend::Handle TopSitesBackend::GetMostVisitedThumbnails(
+    CancelableRequestConsumerBase* consumer,
+    GetMostVisitedThumbnailsCallback* callback) {
+  GetMostVisitedThumbnailsRequest* request =
+      new GetMostVisitedThumbnailsRequest(callback);
+  request->value = new MostVisitedThumbnails;
+  AddRequest(request, consumer);
+  BrowserThread::PostTask(
+      BrowserThread::DB, FROM_HERE, NewRunnableMethod(
+          this,
+          &TopSitesBackend::GetMostVisitedThumbnailsOnDBThread,
+          scoped_refptr<GetMostVisitedThumbnailsRequest>(request)));
+  return request->handle();
+}
+
+void TopSitesBackend::UpdateTopSites(const TopSitesDelta& delta) {
+  BrowserThread::PostTask(
+      BrowserThread::DB, FROM_HERE, NewRunnableMethod(
+          this, &TopSitesBackend::UpdateTopSitesOnDBThread, delta));
+}
+
+void TopSitesBackend::SetPageThumbnail(const MostVisitedURL& url,
+                                       int url_rank,
+                                       const Images& thumbnail) {
+  BrowserThread::PostTask(
+      BrowserThread::DB, FROM_HERE, NewRunnableMethod(
+          this, &TopSitesBackend::SetPageThumbnailOnDBThread, url,
+          url_rank, thumbnail));
+}
+
+void TopSitesBackend::ResetDatabase() {
+  BrowserThread::PostTask(
+      BrowserThread::DB, FROM_HERE, NewRunnableMethod(
+          this, &TopSitesBackend::ResetDatabaseOnDBThread, db_path_));
+}
+
+TopSitesBackend::Handle TopSitesBackend::DoEmptyRequest(
+    CancelableRequestConsumerBase* consumer,
+    EmptyRequestCallback* callback) {
+  EmptyRequestRequest* request = new EmptyRequestRequest(callback);
+  AddRequest(request, consumer);
+  BrowserThread::PostTask(
+      BrowserThread::DB, FROM_HERE, NewRunnableMethod(
+          this,
+          &TopSitesBackend::DoEmptyRequestOnDBThread,
+          scoped_refptr<EmptyRequestRequest>(request)));
+  return request->handle();
+}
+
+TopSitesBackend::~TopSitesBackend() {
+  DCHECK(!db_.get());  // Shutdown should have happened first (which results in
+                       // nulling out db).
+}
+
+void TopSitesBackend::InitDBOnDBThread(const FilePath& path) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
+  if (!db_->Init(path)) {
+    NOTREACHED() << "Failed to initialize database.";
+    db_.reset();
+  }
+}
+
+void TopSitesBackend::ShutdownDBOnDBThread() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
+  db_.reset();
+}
+
+void TopSitesBackend::GetMostVisitedThumbnailsOnDBThread(
+    scoped_refptr<GetMostVisitedThumbnailsRequest> request) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
+
+  if (request->canceled())
+    return;
+
+  bool may_need_history_migration = false;
+  if (db_.get()) {
+    db_->GetPageThumbnails(&(request->value->most_visited),
+                           &(request->value->url_to_images_map));
+    may_need_history_migration = db_->may_need_history_migration();
+  }
+  request->ForwardResult(GetMostVisitedThumbnailsRequest::TupleType(
+                             request->handle(),
+                             request->value,
+                             may_need_history_migration));
+}
+
+void TopSitesBackend::UpdateTopSitesOnDBThread(const TopSitesDelta& delta) {
+  if (!db_.get())
+    return;
+
+  for (size_t i = 0; i < delta.deleted.size(); ++i)
+    db_->RemoveURL(delta.deleted[i]);
+
+  for (size_t i = 0; i < delta.added.size(); ++i)
+    db_->SetPageThumbnail(delta.added[i].url, delta.added[i].rank, Images());
+
+  for (size_t i = 0; i < delta.moved.size(); ++i)
+    db_->UpdatePageRank(delta.moved[i].url, delta.moved[i].rank);
+}
+
+void TopSitesBackend::SetPageThumbnailOnDBThread(const MostVisitedURL& url,
+                                                 int url_rank,
+                                                 const Images& thumbnail) {
+  if (!db_.get())
+    return;
+
+  db_->SetPageThumbnail(url, url_rank, thumbnail);
+}
+
+void TopSitesBackend::ResetDatabaseOnDBThread(const FilePath& file_path) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
+  db_.reset(NULL);
+  file_util::Delete(db_path_, false);
+  db_.reset(new TopSitesDatabase());
+  InitDBOnDBThread(db_path_);
+}
+
+void TopSitesBackend::DoEmptyRequestOnDBThread(
+    scoped_refptr<EmptyRequestRequest> request) {
+  request->ForwardResult(EmptyRequestRequest::TupleType(request->handle()));
+}
+
+}  // namespace history
diff --git a/chrome/browser/history/top_sites_backend.h b/chrome/browser/history/top_sites_backend.h
new file mode 100644
index 0000000..50d0867
--- /dev/null
+++ b/chrome/browser/history/top_sites_backend.h
@@ -0,0 +1,106 @@
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_HISTORY_TOP_SITES_BACKEND_H_
+#define CHROME_BROWSER_HISTORY_TOP_SITES_BACKEND_H_
+#pragma once
+
+#include "base/file_path.h"
+#include "base/ref_counted.h"
+#include "base/scoped_ptr.h"
+#include "chrome/browser/cancelable_request.h"
+#include "chrome/browser/history/history_types.h"
+
+class FilePath;
+
+namespace history {
+
+class TopSitesDatabase;
+
+// Service used by TopSites to have db interaction happen on the DB thread.  All
+// public methods are invoked on the ui thread and get funneled to the DB
+// thread.
+class TopSitesBackend
+    : public base::RefCountedThreadSafe<TopSitesBackend>,
+      public CancelableRequestProvider {
+ public:
+  TopSitesBackend();
+
+  void Init(const FilePath& path);
+
+  // Schedules the db to be shutdown.
+  void Shutdown();
+
+  // The boolean parameter indicates if the DB existed on disk or needs to be
+  // migrated.
+  typedef Callback3<Handle, scoped_refptr<MostVisitedThumbnails>, bool >::Type
+      GetMostVisitedThumbnailsCallback;
+  typedef CancelableRequest1<TopSitesBackend::GetMostVisitedThumbnailsCallback,
+                             scoped_refptr<MostVisitedThumbnails> >
+      GetMostVisitedThumbnailsRequest;
+
+  // Fetches MostVisitedThumbnails.
+  Handle GetMostVisitedThumbnails(CancelableRequestConsumerBase* consumer,
+                                  GetMostVisitedThumbnailsCallback* callback);
+
+  // Updates top sites database from the specified delta.
+  void UpdateTopSites(const TopSitesDelta& delta);
+
+  // Sets the thumbnail.
+  void SetPageThumbnail(const MostVisitedURL& url,
+                        int url_rank,
+                        const Images& thumbnail);
+
+  // Deletes the database and recreates it.
+  void ResetDatabase();
+
+  typedef Callback1<Handle>::Type EmptyRequestCallback;
+  typedef CancelableRequest<TopSitesBackend::EmptyRequestCallback>
+      EmptyRequestRequest;
+
+  // Schedules a request that does nothing on the DB thread, but then notifies
+  // the callback on the calling thread. This is used to make sure the db has
+  // finished processing a request.
+  Handle DoEmptyRequest(CancelableRequestConsumerBase* consumer,
+                        EmptyRequestCallback* callback);
+
+ private:
+  friend class base::RefCountedThreadSafe<TopSitesBackend>;
+
+  ~TopSitesBackend();
+
+  // Invokes Init on the db_.
+  void InitDBOnDBThread(const FilePath& path);
+
+  // Shuts down the db.
+  void ShutdownDBOnDBThread();
+
+  // Does the work of getting the most visted thumbnails.
+  void GetMostVisitedThumbnailsOnDBThread(
+      scoped_refptr<GetMostVisitedThumbnailsRequest> request);
+
+  // Updates top sites.
+  void UpdateTopSitesOnDBThread(const TopSitesDelta& delta);
+
+  // Sets the thumbnail.
+  void SetPageThumbnailOnDBThread(const MostVisitedURL& url,
+                                  int url_rank,
+                                  const Images& thumbnail);
+
+  // Resets the database.
+  void ResetDatabaseOnDBThread(const FilePath& file_path);
+
+  // Notifies the request.
+  void DoEmptyRequestOnDBThread(scoped_refptr<EmptyRequestRequest> request);
+
+  FilePath db_path_;
+
+  scoped_ptr<TopSitesDatabase> db_;
+
+  DISALLOW_COPY_AND_ASSIGN(TopSitesBackend);
+};
+
+}  // namespace history
+
+#endif  // CHROME_BROWSER_HISTORY_TOP_SITES_BACKEND_H_
diff --git a/chrome/browser/history/top_sites_cache.cc b/chrome/browser/history/top_sites_cache.cc
new file mode 100644
index 0000000..828b701
--- /dev/null
+++ b/chrome/browser/history/top_sites_cache.cc
@@ -0,0 +1,110 @@
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/history/top_sites_cache.h"
+
+#include "base/logging.h"
+#include "base/ref_counted_memory.h"
+
+namespace history {
+
+TopSitesCache::TopSitesCache() {
+}
+
+TopSitesCache::~TopSitesCache() {
+}
+
+void TopSitesCache::SetTopSites(const MostVisitedURLList& top_sites) {
+  top_sites_ = top_sites;
+  GenerateCanonicalURLs();
+}
+
+void TopSitesCache::SetThumbnails(const URLToImagesMap& images) {
+  images_ = images;
+}
+
+void TopSitesCache::SetPageThumbnail(const GURL& url,
+                                     RefCountedBytes* thumbnail,
+                                     const ThumbnailScore& score) {
+  Images& img = images_[GetCanonicalURL(url)];
+  img.thumbnail = thumbnail;
+  img.thumbnail_score = score;
+}
+
+Images* TopSitesCache::GetImage(const GURL& url) {
+  return &images_[GetCanonicalURL(url)];
+}
+
+bool TopSitesCache::GetPageThumbnail(const GURL& url,
+                                     scoped_refptr<RefCountedBytes>* bytes) {
+  std::map<GURL, Images>::const_iterator found =
+      images_.find(GetCanonicalURL(url));
+  if (found != images_.end()) {
+    *bytes = found->second.thumbnail.get();
+    return true;
+  }
+  return false;
+}
+
+GURL TopSitesCache::GetCanonicalURL(const GURL& url) {
+  CanonicalURLs::iterator i = TopSitesCache::GetCanonicalURLsIterator(url);
+  return i == canonical_urls_.end() ? url : i->first.first->url;
+}
+
+bool TopSitesCache::IsKnownURL(const GURL& url) {
+  return GetCanonicalURLsIterator(url) != canonical_urls_.end();
+}
+
+size_t TopSitesCache::GetURLIndex(const GURL& url) {
+  DCHECK(IsKnownURL(url));
+  return GetCanonicalURLsIterator(url)->second;
+}
+
+void TopSitesCache::RemoveUnreferencedThumbnails() {
+  for (URLToImagesMap::iterator i = images_.begin(); i != images_.end(); ) {
+    if (IsKnownURL(i->first)) {
+      ++i;
+    } else {
+      URLToImagesMap::iterator next_i = i;
+      ++next_i;
+      images_.erase(i);
+      i = next_i;
+    }
+  }
+}
+
+void TopSitesCache::GenerateCanonicalURLs() {
+  canonical_urls_.clear();
+  for (size_t i = 0; i < top_sites_.size(); i++)
+    StoreRedirectChain(top_sites_[i].redirects, i);
+}
+
+void TopSitesCache::StoreRedirectChain(const RedirectList& redirects,
+                                       size_t destination) {
+  // redirects is empty if the user pinned a site and there are not enough top
+  // sites before the pinned site.
+
+  // Map all the redirected URLs to the destination.
+  for (size_t i = 0; i < redirects.size(); i++) {
+    // If this redirect is already known, don't replace it with a new one.
+    if (!IsKnownURL(redirects[i])) {
+      CanonicalURLEntry entry;
+      entry.first = &(top_sites_[destination]);
+      entry.second = i;
+      canonical_urls_[entry] = destination;
+    }
+  }
+}
+
+TopSitesCache::CanonicalURLs::iterator TopSitesCache::GetCanonicalURLsIterator(
+    const GURL& url) {
+  MostVisitedURL most_visited_url;
+  most_visited_url.redirects.push_back(url);
+  CanonicalURLEntry entry;
+  entry.first = &most_visited_url;
+  entry.second = 0u;
+  return canonical_urls_.find(entry);
+}
+
+}  // namespace history
diff --git a/chrome/browser/history/top_sites_cache.h b/chrome/browser/history/top_sites_cache.h
new file mode 100644
index 0000000..4c5d79a
--- /dev/null
+++ b/chrome/browser/history/top_sites_cache.h
@@ -0,0 +1,108 @@
+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_HISTORY_TOP_SITES_CACHE_H_
+#define CHROME_BROWSER_HISTORY_TOP_SITES_CACHE_H_
+#pragma once
+
+#include <algorithm>
+#include <map>
+#include <string>
+
+#include "base/ref_counted.h"
+#include "chrome/browser/history/history_types.h"
+
+class RefCountedBytes;
+
+namespace history {
+
+// TopSitesCache caches the top sites and thumbnails for TopSites.
+class TopSitesCache {
+ public:
+  TopSitesCache();
+  ~TopSitesCache();
+
+  // The top sites.
+  void SetTopSites(const MostVisitedURLList& top_sites);
+  const MostVisitedURLList& top_sites() const { return top_sites_; }
+
+  // The thumbnails.
+  void SetThumbnails(const URLToImagesMap& images);
+  const URLToImagesMap& images() const { return images_; }
+
+  // Set a thumbnail.
+  void SetPageThumbnail(const GURL& url,
+                        RefCountedBytes* thumbnail,
+                        const ThumbnailScore& score);
+
+  // Returns the thumbnail as an Image for the specified url. This adds an entry
+  // for |url| if one has not yet been added.
+  Images* GetImage(const GURL& url);
+
+  // Fetches the thumbnail for the specified url. Returns true if there is a
+  // thumbnail for the specified url.
+  bool GetPageThumbnail(const GURL& url,
+                        scoped_refptr<RefCountedBytes>* bytes);
+
+  // Returns the canonical URL for |url|.
+  GURL GetCanonicalURL(const GURL& url);
+
+  // Returns true if |url| is known.
+  bool IsKnownURL(const GURL& url);
+
+  // Returns the index into |top_sites_| for |url|.
+  size_t GetURLIndex(const GURL& url);
+
+  // Removes any thumbnails that are no longer referenced by the top sites.
+  void RemoveUnreferencedThumbnails();
+
+ private:
+  // The entries in CanonicalURLs, see CanonicalURLs for details. The second
+  // argument gives the index of the URL into MostVisitedURLs redirects.
+  typedef std::pair<MostVisitedURL*, size_t> CanonicalURLEntry;
+
+  // Comparator used for CanonicalURLs.
+  class CanonicalURLComparator {
+   public:
+    bool operator()(const CanonicalURLEntry& e1,
+                    const CanonicalURLEntry& e2) const {
+      return e1.first->redirects[e1.second] < e2.first->redirects[e2.second];
+    }
+  };
+
+  // This is used to map from redirect url to the MostVisitedURL the redirect is
+  // from. Ideally this would be map<GURL, size_t> (second param indexing into
+  // top_sites_), but this results in duplicating all redirect urls. As some
+  // sites have a lot of redirects, we instead use the MostVisitedURL* and the
+  // index of the redirect as the key, and the index into top_sites_ as the
+  // value. This way we aren't duplicating GURLs. CanonicalURLComparator
+  // enforces the ordering as if we were using GURLs.
+  typedef std::map<CanonicalURLEntry, size_t,
+                   CanonicalURLComparator> CanonicalURLs;
+
+  // Generates the set of canonical urls from |top_sites_|.
+  void GenerateCanonicalURLs();
+
+  // Stores a set of redirects. This is used by GenerateCanonicalURLs.
+  void StoreRedirectChain(const RedirectList& redirects, size_t destination);
+
+  // Returns the iterator into canconical_urls_ for the specified url.
+  CanonicalURLs::iterator GetCanonicalURLsIterator(const GURL& url);
+
+  // The top sites.
+  MostVisitedURLList top_sites_;
+
+  // The images. These map from canonical url to image.
+  URLToImagesMap images_;
+
+  // Generated from the redirects to and from the most visited pages. See
+  // description above typedef for details.
+  CanonicalURLs canonical_urls_;
+
+  DISALLOW_COPY_AND_ASSIGN(TopSitesCache);
+};
+
+}  // namespace history
+
+#endif  // CHROME_BROWSER_HISTORY_TOP_SITES_CACHE_H_
diff --git a/chrome/browser/history/top_sites_database.cc b/chrome/browser/history/top_sites_database.cc
index 05a588a..8bfbcaf 100644
--- a/chrome/browser/history/top_sites_database.cc
+++ b/chrome/browser/history/top_sites_database.cc
@@ -2,7 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "app/sql/connection.h"
 #include "app/sql/transaction.h"
+#include "base/file_util.h"
 #include "base/string_util.h"
 #include "chrome/browser/diagnostics/sqlite_diagnostics.h"
 #include "chrome/browser/history/history_types.h"
@@ -11,56 +13,85 @@
 
 namespace history {
 
-TopSitesDatabaseImpl::TopSitesDatabaseImpl() {
+static const int kVersionNumber = 1;
+
+TopSitesDatabase::TopSitesDatabase() : may_need_history_migration_(false) {
 }
 
-TopSitesDatabaseImpl::~TopSitesDatabaseImpl() {
+TopSitesDatabase::~TopSitesDatabase() {
 }
 
-bool TopSitesDatabaseImpl::Init(const FilePath& db_name) {
-  // Settings copied from ThumbnailDatabase.
-  db_.set_error_delegate(GetErrorHandlerForThumbnailDb());
-  db_.set_page_size(4096);
-  db_.set_cache_size(64);
+bool TopSitesDatabase::Init(const FilePath& db_name) {
+  bool file_existed = file_util::PathExists(db_name);
+
+  if (!file_existed)
+    may_need_history_migration_ = true;
 
-  if (!db_.Open(db_name)) {
-    LOG(WARNING) << db_.GetErrorMessage();
+  db_.reset(CreateDB(db_name));
+  if (!db_.get())
     return false;
+
+  bool does_meta_exist = sql::MetaTable::DoesTableExist(db_.get());
+  if (!does_meta_exist && file_existed) {
+    may_need_history_migration_ = true;
+
+    // If the meta file doesn't exist, this version is old. We could remove all
+    // the entries as they are no longer applicable, but it's safest to just
+    // remove the file and start over.
+    db_.reset(NULL);
+    if (!file_util::Delete(db_name, false) &&
+        !file_util::Delete(db_name, false)) {
+      // Try to delete twice. If we can't, fail.
+      LOG(ERROR) << "unable to delete old TopSites file";
+      return false;
+    }
+    db_.reset(CreateDB(db_name));
+    if (!db_.get())
+      return false;
   }
 
-  return InitThumbnailTable();
+  if (!meta_table_.Init(db_.get(), kVersionNumber, kVersionNumber))
+    return false;
+
+  if (!InitThumbnailTable())
+    return false;
+
+  // Version check.
+  if (meta_table_.GetVersionNumber() != kVersionNumber)
+    return false;
+
+  return true;
 }
 
-bool TopSitesDatabaseImpl::InitThumbnailTable() {
-  if (!db_.DoesTableExist("thumbnails")) {
-    if (!db_.Execute("CREATE TABLE thumbnails ("
-                     "url LONGVARCHAR PRIMARY KEY,"
-                     "url_rank INTEGER ,"
-                     "title LONGVARCHAR,"
-                     "thumbnail BLOB,"
-                     "redirects LONGVARCHAR,"
-                     "boring_score DOUBLE DEFAULT 1.0, "
-                     "good_clipping INTEGER DEFAULT 0, "
-                     "at_top INTEGER DEFAULT 0, "
-                     "last_updated INTEGER DEFAULT 0) ")) {
-      LOG(WARNING) << db_.GetErrorMessage();
+bool TopSitesDatabase::InitThumbnailTable() {
+  if (!db_->DoesTableExist("thumbnails")) {
+    if (!db_->Execute("CREATE TABLE thumbnails ("
+                      "url LONGVARCHAR PRIMARY KEY,"
+                      "url_rank INTEGER ,"
+                      "title LONGVARCHAR,"
+                      "thumbnail BLOB,"
+                      "redirects LONGVARCHAR,"
+                      "boring_score DOUBLE DEFAULT 1.0, "
+                      "good_clipping INTEGER DEFAULT 0, "
+                      "at_top INTEGER DEFAULT 0, "
+                      "last_updated INTEGER DEFAULT 0) ")) {
+      LOG(WARNING) << db_->GetErrorMessage();
       return false;
     }
   }
   return true;
 }
 
-void TopSitesDatabaseImpl::GetPageThumbnails(MostVisitedURLList* urls,
-                                             std::map<GURL,
-                                             Images>* thumbnails) {
-  sql::Statement statement(db_.GetCachedStatement(
+void TopSitesDatabase::GetPageThumbnails(MostVisitedURLList* urls,
+                                             URLToImagesMap* thumbnails) {
+  sql::Statement statement(db_->GetCachedStatement(
       SQL_FROM_HERE,
       "SELECT url, url_rank, title, thumbnail, redirects, "
       "boring_score, good_clipping, at_top, last_updated "
       "FROM thumbnails ORDER BY url_rank "));
 
   if (!statement) {
-    LOG(WARNING) << db_.GetErrorMessage();
+    LOG(WARNING) << db_->GetErrorMessage();
     return;
   }
 
@@ -92,7 +123,7 @@ void TopSitesDatabaseImpl::GetPageThumbnails(MostVisitedURLList* urls,
 }
 
 // static
-std::string TopSitesDatabaseImpl::GetRedirects(const MostVisitedURL& url) {
+std::string TopSitesDatabase::GetRedirects(const MostVisitedURL& url) {
   std::vector<std::string> redirects;
   for (size_t i = 0; i < url.redirects.size(); i++)
     redirects.push_back(url.redirects[i].spec());
@@ -100,18 +131,18 @@ std::string TopSitesDatabaseImpl::GetRedirects(const MostVisitedURL& url) {
 }
 
 // static
-void TopSitesDatabaseImpl::SetRedirects(const std::string& redirects,
-                                        MostVisitedURL* url) {
+void TopSitesDatabase::SetRedirects(const std::string& redirects,
+                                    MostVisitedURL* url) {
   std::vector<std::string> redirects_vector;
   SplitStringAlongWhitespace(redirects, &redirects_vector);
   for (size_t i = 0; i < redirects_vector.size(); i++)
     url->redirects.push_back(GURL(redirects_vector[i]));
 }
 
-void TopSitesDatabaseImpl::SetPageThumbnail(const MostVisitedURL& url,
+void TopSitesDatabase::SetPageThumbnail(const MostVisitedURL& url,
                                             int new_rank,
                                             const Images& thumbnail) {
-  sql::Transaction transaction(&db_);
+  sql::Transaction transaction(db_.get());
   transaction.Begin();
 
   int rank = GetURLRank(url);
@@ -125,9 +156,9 @@ void TopSitesDatabaseImpl::SetPageThumbnail(const MostVisitedURL& url,
   transaction.Commit();
 }
 
-void TopSitesDatabaseImpl::UpdatePageThumbnail(
+void TopSitesDatabase::UpdatePageThumbnail(
     const MostVisitedURL& url, const Images& thumbnail) {
-  sql::Statement statement(db_.GetCachedStatement(
+  sql::Statement statement(db_->GetCachedStatement(
       SQL_FROM_HERE,
       "UPDATE thumbnails SET "
       "title = ?, thumbnail = ?, redirects = ?, "
@@ -137,9 +168,9 @@ void TopSitesDatabaseImpl::UpdatePageThumbnail(
     return;
 
   statement.BindString16(0, url.title);
-  if (thumbnail.thumbnail.get()) {
-    statement.BindBlob(1, &thumbnail.thumbnail->data.front(),
-                       static_cast<int>(thumbnail.thumbnail->data.size()));
+  if (thumbnail.thumbnail.get() && thumbnail.thumbnail->front()) {
+    statement.BindBlob(1, thumbnail.thumbnail->front(),
+                       static_cast<int>(thumbnail.thumbnail->size()));
   }
   statement.BindString(2, GetRedirects(url));
   const ThumbnailScore& score = thumbnail.thumbnail_score;
@@ -149,15 +180,15 @@ void TopSitesDatabaseImpl::UpdatePageThumbnail(
   statement.BindInt64(6, score.time_at_snapshot.ToInternalValue());
   statement.BindString(7, url.url.spec());
   if (!statement.Run())
-    NOTREACHED() << db_.GetErrorMessage();
+    NOTREACHED() << db_->GetErrorMessage();
 }
 
-void TopSitesDatabaseImpl::AddPageThumbnail(const MostVisitedURL& url,
+void TopSitesDatabase::AddPageThumbnail(const MostVisitedURL& url,
                                             int new_rank,
                                             const Images& thumbnail) {
   int count = GetRowCount();
 
-  sql::Statement statement(db_.GetCachedStatement(
+  sql::Statement statement(db_->GetCachedStatement(
       SQL_FROM_HERE,
       "INSERT OR REPLACE INTO thumbnails "
       "(url, url_rank, title, thumbnail, redirects, "
@@ -169,9 +200,9 @@ void TopSitesDatabaseImpl::AddPageThumbnail(const MostVisitedURL& url,
   statement.BindString(0, url.url.spec());
   statement.BindInt(1, count);  // Make it the last url.
   statement.BindString16(2, url.title);
-  if (thumbnail.thumbnail.get()) {
-    statement.BindBlob(3, &thumbnail.thumbnail->data.front(),
-                       static_cast<int>(thumbnail.thumbnail->data.size()));
+  if (thumbnail.thumbnail.get() && thumbnail.thumbnail->front()) {
+    statement.BindBlob(3, thumbnail.thumbnail->front(),
+                       static_cast<int>(thumbnail.thumbnail->size()));
   }
   statement.BindString(4, GetRedirects(url));
   const ThumbnailScore& score = thumbnail.thumbnail_score;
@@ -180,21 +211,21 @@ void TopSitesDatabaseImpl::AddPageThumbnail(const MostVisitedURL& url,
   statement.BindBool(7, score.at_top);
   statement.BindInt64(8, score.time_at_snapshot.ToInternalValue());
   if (!statement.Run())
-    NOTREACHED() << db_.GetErrorMessage();
+    NOTREACHED() << db_->GetErrorMessage();
 
   UpdatePageRankNoTransaction(url, new_rank);
 }
 
-void TopSitesDatabaseImpl::UpdatePageRank(const MostVisitedURL& url,
+void TopSitesDatabase::UpdatePageRank(const MostVisitedURL& url,
                                           int new_rank) {
-  sql::Transaction transaction(&db_);
+  sql::Transaction transaction(db_.get());
   transaction.Begin();
   UpdatePageRankNoTransaction(url, new_rank);
   transaction.Commit();
 }
 
 // Caller should have a transaction open.
-void TopSitesDatabaseImpl::UpdatePageRankNoTransaction(
+void TopSitesDatabase::UpdatePageRankNoTransaction(
     const MostVisitedURL& url, int new_rank) {
   int prev_rank = GetURLRank(url);
   if (prev_rank == -1) {
@@ -205,7 +236,7 @@ void TopSitesDatabaseImpl::UpdatePageRankNoTransaction(
   // Shift the ranks.
   if (prev_rank > new_rank) {
     // Shift up
-    sql::Statement shift_statement(db_.GetCachedStatement(
+    sql::Statement shift_statement(db_->GetCachedStatement(
         SQL_FROM_HERE,
         "UPDATE thumbnails "
         "SET url_rank = url_rank + 1 "
@@ -216,7 +247,7 @@ void TopSitesDatabaseImpl::UpdatePageRankNoTransaction(
       shift_statement.Run();
   } else if (prev_rank < new_rank) {
     // Shift down
-    sql::Statement shift_statement(db_.GetCachedStatement(
+    sql::Statement shift_statement(db_->GetCachedStatement(
         SQL_FROM_HERE,
         "UPDATE thumbnails "
         "SET url_rank = url_rank - 1 "
@@ -228,7 +259,7 @@ void TopSitesDatabaseImpl::UpdatePageRankNoTransaction(
   }
 
   // Set the url's rank.
-  sql::Statement set_statement(db_.GetCachedStatement(
+  sql::Statement set_statement(db_->GetCachedStatement(
       SQL_FROM_HERE,
       "UPDATE thumbnails "
       "SET url_rank = ? "
@@ -239,15 +270,15 @@ void TopSitesDatabaseImpl::UpdatePageRankNoTransaction(
     set_statement.Run();
 }
 
-bool TopSitesDatabaseImpl::GetPageThumbnail(const GURL& url,
+bool TopSitesDatabase::GetPageThumbnail(const GURL& url,
                                             Images* thumbnail) {
-  sql::Statement statement(db_.GetCachedStatement(
+  sql::Statement statement(db_->GetCachedStatement(
       SQL_FROM_HERE,
       "SELECT thumbnail, boring_score, good_clipping, at_top, last_updated "
       "FROM thumbnails WHERE url=?"));
 
   if (!statement) {
-    LOG(WARNING) << db_.GetErrorMessage();
+    LOG(WARNING) << db_->GetErrorMessage();
     return false;
   }
 
@@ -266,13 +297,13 @@ bool TopSitesDatabaseImpl::GetPageThumbnail(const GURL& url,
   return true;
 }
 
-int TopSitesDatabaseImpl::GetRowCount() {
+int TopSitesDatabase::GetRowCount() {
   int result = 0;
-  sql::Statement select_statement(db_.GetCachedStatement(
+  sql::Statement select_statement(db_->GetCachedStatement(
       SQL_FROM_HERE,
       "SELECT COUNT (url) FROM thumbnails"));
   if (!select_statement) {
-    LOG(WARNING) << db_.GetErrorMessage();
+    LOG(WARNING) << db_->GetErrorMessage();
     return result;
   }
 
@@ -282,14 +313,14 @@ int TopSitesDatabaseImpl::GetRowCount() {
   return result;
 }
 
-int TopSitesDatabaseImpl::GetURLRank(const MostVisitedURL& url) {
+int TopSitesDatabase::GetURLRank(const MostVisitedURL& url) {
   int result = -1;
-  sql::Statement select_statement(db_.GetCachedStatement(
+  sql::Statement select_statement(db_->GetCachedStatement(
       SQL_FROM_HERE,
       "SELECT url_rank "
       "FROM thumbnails WHERE url=?"));
   if (!select_statement) {
-    LOG(WARNING) << db_.GetErrorMessage();
+    LOG(WARNING) << db_->GetErrorMessage();
     return result;
   }
 
@@ -301,15 +332,15 @@ int TopSitesDatabaseImpl::GetURLRank(const MostVisitedURL& url) {
 }
 
 // Remove the record for this URL. Returns true iff removed successfully.
-bool TopSitesDatabaseImpl::RemoveURL(const MostVisitedURL& url) {
+bool TopSitesDatabase::RemoveURL(const MostVisitedURL& url) {
   int old_rank = GetURLRank(url);
   if (old_rank < 0)
     return false;
 
-  sql::Transaction transaction(&db_);
+  sql::Transaction transaction(db_.get());
   transaction.Begin();
   // Decrement all following ranks.
-  sql::Statement shift_statement(db_.GetCachedStatement(
+  sql::Statement shift_statement(db_->GetCachedStatement(
       SQL_FROM_HERE,
       "UPDATE thumbnails "
       "SET url_rank = url_rank - 1 "
@@ -320,8 +351,8 @@ bool TopSitesDatabaseImpl::RemoveURL(const MostVisitedURL& url) {
   shift_statement.Run();
 
   sql::Statement delete_statement(
-      db_.GetCachedStatement(SQL_FROM_HERE,
-                             "DELETE FROM thumbnails WHERE url = ?"));
+      db_->GetCachedStatement(SQL_FROM_HERE,
+                              "DELETE FROM thumbnails WHERE url = ?"));
   if (!delete_statement)
     return false;
   delete_statement.BindString(0, url.url.spec());
@@ -330,4 +361,19 @@ bool TopSitesDatabaseImpl::RemoveURL(const MostVisitedURL& url) {
   return transaction.Commit();
 }
 
+sql::Connection* TopSitesDatabase::CreateDB(const FilePath& db_name) {
+  scoped_ptr<sql::Connection> db(new sql::Connection());
+  // Settings copied from ThumbnailDatabase.
+  db->set_error_delegate(GetErrorHandlerForThumbnailDb());
+  db->set_page_size(4096);
+  db->set_cache_size(32);
+
+  if (!db->Open(db_name)) {
+    LOG(ERROR) << db->GetErrorMessage();
+    return NULL;
+  }
+
+  return db.release();
+}
+
 }  // namespace history
diff --git a/chrome/browser/history/top_sites_database.h b/chrome/browser/history/top_sites_database.h
index edfb4e5..8450889 100644
--- a/chrome/browser/history/top_sites_database.h
+++ b/chrome/browser/history/top_sites_database.h
@@ -9,94 +9,61 @@
 #include <map>
 #include <string>
 
-#include "app/sql/connection.h"
+#include "app/sql/meta_table.h"
 #include "base/ref_counted.h"
+#include "chrome/browser/history/history_types.h"
 #include "chrome/browser/history/url_database.h"  // For DBCloseScoper.
 
 class FilePath;
 class RefCountedMemory;
 class SkBitmap;
-class Images;
 
-namespace base {
-class Time;
+namespace app {
+class Connection;
 }
 
 namespace history {
 
-// Interface to be implemented by the real storage layer as well as
-// the mockup database for testing.
 class TopSitesDatabase {
  public:
-  virtual ~TopSitesDatabase() {}
-  virtual bool Init(const FilePath& filename) {
-    return true;
-  }
-
-  // Returns a list of all URLs currently in the table.
-  virtual void GetPageThumbnails(MostVisitedURLList* urls,
-                                 std::map<GURL,
-                                 Images>* thumbnails) = 0;
-
-  // Set a thumbnail for a URL. |url_rank| is the position of the URL
-  // in the list of TopURLs, zero-based.
-  // If the URL is not in the table, add it. If it is, replace its
-  // thumbnail.
-  virtual void SetPageThumbnail(const MostVisitedURL& url,
-                                int url_rank,
-                                const Images& thumbnail) = 0;
-
-  // Update rank of a URL that's already in the database.
-  virtual void UpdatePageRank(const MostVisitedURL& url, int new_rank) = 0;
-
-  // Convenience wrapper.
-  bool GetPageThumbnail(const MostVisitedURL& url,
-                        Images* thumbnail) {
-    return GetPageThumbnail(url.url, thumbnail);
-  }
-
-  // Get a thumbnail for a given page. Returns true iff we have the thumbnail.
-  virtual bool GetPageThumbnail(const GURL& url,
-                                Images* thumbnail) = 0;
-
-  // Remove the record for this URL. Returns true iff removed successfully.
-  virtual bool RemoveURL(const MostVisitedURL& url) = 0;
-};
-
-class TopSitesDatabaseImpl : public TopSitesDatabase {
- public:
-  TopSitesDatabaseImpl();
-  virtual ~TopSitesDatabaseImpl();
+  TopSitesDatabase();
+  ~TopSitesDatabase();
 
   // Must be called after creation but before any other methods are called.
   // Returns true on success. If false, no other functions should be called.
-  virtual bool Init(const FilePath& db_name);
+  bool Init(const FilePath& db_name);
+
+  // Returns true if migration of top sites from history may be needed. A value
+  // of true means either migration is definitely needed (the top sites file is
+  // old) or doesn't exist (as would happen for a new user).
+  bool may_need_history_migration() const {
+    return may_need_history_migration_;
+  }
 
   // Thumbnails ----------------------------------------------------------------
 
   // Returns a list of all URLs currently in the table.
   // WARNING: clears both input arguments.
-  virtual void GetPageThumbnails(MostVisitedURLList* urls,
-                                 std::map<GURL, Images>* thumbnails);
+  void GetPageThumbnails(MostVisitedURLList* urls,
+                         std::map<GURL, Images>* thumbnails);
 
   // Set a thumbnail for a URL. |url_rank| is the position of the URL
   // in the list of TopURLs, zero-based.
   // If the URL is not in the table, add it. If it is, replace its
   // thumbnail and rank. Shift the ranks of other URLs if necessary.
-  virtual void SetPageThumbnail(const MostVisitedURL& url,
-                                int new_rank,
-                                const Images& thumbnail);
+  void SetPageThumbnail(const MostVisitedURL& url,
+                        int new_rank,
+                        const Images& thumbnail);
 
   // Sets the rank for a given URL. The URL must be in the database.
   // Use SetPageThumbnail if it's not.
-  virtual void UpdatePageRank(const MostVisitedURL& url, int new_rank);
+  void UpdatePageRank(const MostVisitedURL& url, int new_rank);
 
   // Get a thumbnail for a given page. Returns true iff we have the thumbnail.
-  virtual bool GetPageThumbnail(const GURL& url,
-                                Images* thumbnail);
+  bool GetPageThumbnail(const GURL& url, Images* thumbnail);
 
   // Remove the record for this URL. Returns true iff removed successfully.
-  virtual bool RemoveURL(const MostVisitedURL& url);
+  bool RemoveURL(const MostVisitedURL& url);
 
  private:
   // Creates the thumbnail table, returning true if the table already exists
@@ -121,13 +88,21 @@ class TopSitesDatabaseImpl : public TopSitesDatabase {
   // Returns the number of URLs (rows) in the database.
   int GetRowCount();
 
+  sql::Connection* CreateDB(const FilePath& db_name);
+
   // Encodes redirects into a string.
   static std::string GetRedirects(const MostVisitedURL& url);
 
   // Decodes redirects from a string and sets them for the url.
   static void SetRedirects(const std::string& redirects, MostVisitedURL* url);
 
-  sql::Connection db_;
+  scoped_ptr<sql::Connection> db_;
+  sql::MetaTable meta_table_;
+
+  // See description above class.
+  bool may_need_history_migration_;
+
+  DISALLOW_COPY_AND_ASSIGN(TopSitesDatabase);
 };
 
 }  // namespace history
diff --git a/chrome/browser/history/top_sites_unittest.cc b/chrome/browser/history/top_sites_unittest.cc
index 160b275..f908646 100644
--- a/chrome/browser/history/top_sites_unittest.cc
+++ b/chrome/browser/history/top_sites_unittest.cc
@@ -3,18 +3,26 @@
 // found in the LICENSE file.
 
 #include "app/l10n_util.h"
+#include "base/command_line.h"
 #include "base/file_util.h"
+#include "base/path_service.h"
 #include "base/scoped_temp_dir.h"
 #include "base/string_util.h"
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/browser/browser_thread.h"
-#include "chrome/browser/history/top_sites.h"
 #include "chrome/browser/dom_ui/most_visited_handler.h"
+#include "chrome/browser/history/history_backend.h"
+#include "chrome/browser/history/history_database.h"
 #include "chrome/browser/history/history_marshaling.h"
-#include "chrome/browser/history/top_sites_database.h"
 #include "chrome/browser/history/history_notifications.h"
+#include "chrome/browser/history/top_sites.h"
+#include "chrome/browser/history/top_sites_backend.h"
+#include "chrome/browser/history/top_sites_cache.h"
+#include "chrome/browser/history/top_sites_database.h"
+#include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_paths.h"
+#include "chrome/common/chrome_switches.h"
 #include "chrome/test/testing_profile.h"
 #include "chrome/tools/profiles/thumbnail-inl.h"
 #include "gfx/codec/jpeg_codec.h"
@@ -25,246 +33,362 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 
-
 namespace history {
 
-static const unsigned char kBlob[] =
-    "12346102356120394751634516591348710478123649165419234519234512349134";
+namespace {
 
-class TopSitesTest : public testing::Test {
+// Used by WaitForHistory, see it for details.
+class WaitForHistoryTask : public HistoryDBTask {
  public:
-  TopSitesTest() : number_of_callbacks_(0) {
+  WaitForHistoryTask() {}
+
+  virtual bool RunOnDBThread(HistoryBackend* backend, HistoryDatabase* db) {
+    return true;
   }
-  ~TopSitesTest() {
+
+  virtual void DoneRunOnMainThread() {
+    MessageLoop::current()->Quit();
   }
 
-  TopSites& top_sites() { return *top_sites_; }
-  MostVisitedURLList& urls() { return urls_; }
-  Profile& profile() {return *profile_;}
-  FilePath& file_name() { return file_name_; }
-  RefCountedBytes* google_thumbnail() { return google_thumbnail_; }
-  RefCountedBytes* random_thumbnail() { return random_thumbnail_; }
-  RefCountedBytes* weewar_thumbnail() { return weewar_thumbnail_; }
-  CancelableRequestConsumer* consumer() { return &consumer_; }
-  size_t number_of_callbacks() {return number_of_callbacks_; }
-  // Prepopulated URLs - added at the back of TopSites.
-  GURL welcome_url() {
-    return GURL(l10n_util::GetStringUTF8(IDS_CHROME_WELCOME_URL));
+ private:
+  DISALLOW_COPY_AND_ASSIGN(WaitForHistoryTask);
+};
+
+// Used for querying top sites. Either runs sequentially, or runs a nested
+// nested message loop until the response is complete. The later is used when
+// TopSites is queried before it finishes loading.
+class TopSitesQuerier {
+ public:
+  TopSitesQuerier() : number_of_callbacks_(0), waiting_(false) {}
+
+  // Queries top sites. If |wait| is true a nested message loop is run until the
+  // callback is notified.
+  void QueryTopSites(TopSites* top_sites, bool wait) {
+    int start_number_of_callbacks = number_of_callbacks_;
+    top_sites->GetMostVisitedURLs(
+        &consumer_,
+        NewCallback(this, &TopSitesQuerier::OnTopSitesAvailable));
+    if (wait && start_number_of_callbacks == number_of_callbacks_) {
+      waiting_ = true;
+      MessageLoop::current()->Run();
+    }
   }
-  GURL themes_url() {
-    return GURL(l10n_util::GetStringUTF8(IDS_THEMES_GALLERY_URL));
+
+  void CancelRequest() {
+    consumer_.CancelAllRequests();
+  }
+
+  void set_urls(const MostVisitedURLList& urls) { urls_ = urls; }
+  const MostVisitedURLList& urls() const { return urls_; }
+
+  int number_of_callbacks() const { return number_of_callbacks_; }
+
+ private:
+  // Callback for TopSites::GetMostVisitedURLs.
+  void OnTopSitesAvailable(const history::MostVisitedURLList& data) {
+    urls_ = data;
+    number_of_callbacks_++;
+    if (waiting_) {
+      MessageLoop::current()->Quit();
+      waiting_ = false;
+    }
+  }
+
+  CancelableRequestConsumer consumer_;
+  MostVisitedURLList urls_;
+  int number_of_callbacks_;
+  bool waiting_;
+
+  DISALLOW_COPY_AND_ASSIGN(TopSitesQuerier);
+};
+
+// Extracts the data from |t1| into a SkBitmap. This is intended for usage of
+// thumbnail data, which is stored as jpgs.
+SkBitmap ExtractThumbnail(const RefCountedBytes& t1) {
+  scoped_ptr<SkBitmap> image(gfx::JPEGCodec::Decode(t1.front(),
+                                                    t1.data.size()));
+  return image.get() ? *image : SkBitmap();
+}
+
+// Returns true if t1 and t2 contain the same data.
+bool ThumbnailsAreEqual(RefCountedBytes* t1, RefCountedBytes* t2) {
+  if (!t1 || !t2)
+    return false;
+  if (t1->data.size() != t2->data.size())
+    return false;
+  return std::equal(t1->data.begin(),
+                    t1->data.end(),
+                    t2->data.begin());
+}
+
+}  // namespace
+
+class TopSitesTest : public testing::Test {
+ public:
+  TopSitesTest()
+      : ui_thread_(BrowserThread::UI, &message_loop_),
+        db_thread_(BrowserThread::DB, &message_loop_),
+        original_command_line_(*CommandLine::ForCurrentProcess()) {
   }
 
   virtual void SetUp() {
+    CommandLine::ForCurrentProcess()->AppendSwitch(switches::kEnableTopSites);
     profile_.reset(new TestingProfile);
-    top_sites_ = new TopSites(profile_.get());
-
-    ASSERT_TRUE(temp_dir_.CreateUniqueTempDir());
-    file_name_ = temp_dir_.path().AppendASCII("TopSites.db");
-    EXPECT_TRUE(file_util::Delete(file_name_, false));
-
-    std::vector<unsigned char> random_data(kBlob, kBlob + sizeof(kBlob));
-    std::vector<unsigned char> google_data(kGoogleThumbnail,
-                                           kGoogleThumbnail +
-                                           sizeof(kGoogleThumbnail));
-    std::vector<unsigned char> weewar_data(kWeewarThumbnail,
-                                           kWeewarThumbnail +
-                                           sizeof(kWeewarThumbnail));
-    random_thumbnail_ = new RefCountedBytes(random_data);
-    google_thumbnail_ = new RefCountedBytes(google_data);
-    weewar_thumbnail_ = new RefCountedBytes(weewar_data);
+    if (CreateHistoryAndTopSites()) {
+      profile_->CreateHistoryService(false, false);
+      profile_->CreateTopSites();
+      profile_->BlockUntilTopSitesLoaded();
+    }
   }
 
   virtual void TearDown() {
     profile_.reset();
-    TopSites::DeleteTopSites(top_sites_);
-    EXPECT_TRUE(file_util::Delete(file_name_, false));
+    *CommandLine::ForCurrentProcess() = original_command_line_;
   }
 
-  // Callback for TopSites::GetMostVisitedURLs.
-  void OnTopSitesAvailable(history::MostVisitedURLList data) {
-    urls_ = data;
-    number_of_callbacks_++;
+  // Returns true if history and top sites should be created in SetUp.
+  virtual bool CreateHistoryAndTopSites() {
+    return true;
   }
 
-  // Wrappers that allow private TopSites functions to be called from the
-  // individual tests without making them all be friends.
-  GURL GetCanonicalURL(const GURL& url) const {
-    AutoLock lock(top_sites_->lock_);  // The function asserts it's in the lock.
-    return top_sites_->GetCanonicalURL(url);
+  // Gets the thumbnail for |url| from TopSites.
+  SkBitmap GetThumbnail(const GURL& url) {
+    scoped_refptr<RefCountedBytes> data;
+    return top_sites()->GetPageThumbnail(url, &data) ?
+        ExtractThumbnail(*data.get()) : SkBitmap();
   }
 
-  void StoreMostVisited(std::vector<MostVisitedURL>* urls) {
-    top_sites_->StoreMostVisited(urls);
+  // Creates a bitmap of the specified color.
+  SkBitmap CreateBitmap(SkColor color) {
+    SkBitmap thumbnail;
+    thumbnail.setConfig(SkBitmap::kARGB_8888_Config, 4, 4);
+    thumbnail.allocPixels();
+    thumbnail.eraseColor(color);
+    return thumbnail;
   }
 
-  static void DiffMostVisited(const std::vector<MostVisitedURL>& old_list,
-                              const std::vector<MostVisitedURL>& new_list,
-                              std::vector<size_t>* added_urls,
-                              std::vector<size_t>* deleted_urls,
-                              std::vector<size_t>* moved_urls)  {
-    TopSites::DiffMostVisited(old_list, new_list,
-                              added_urls, deleted_urls, moved_urls);
+  // Forces top sites to load top sites from history, then recreates top sites.
+  // Recreating top sites makes sure the changes from history are saved and
+  // loaded from the db.
+  void RefreshTopSitesAndRecreate() {
+    StartQueryForMostVisited();
+    WaitForHistory();
+    RecreateTopSitesAndBlock();
   }
 
-  Lock& lock() {
-    return top_sites_->lock_;
+  // Blocks the caller until history processes a task. This is useful if you
+  // need to wait until you know history has processed a task.
+  void WaitForHistory() {
+    history_service()->ScheduleDBTask(new WaitForHistoryTask(), &consumer_);
+    MessageLoop::current()->Run();
   }
 
- private:
-  scoped_refptr<TopSites> top_sites_;
-  MostVisitedURLList urls_;
-  size_t number_of_callbacks_;
-  scoped_ptr<TestingProfile> profile_;
-  ScopedTempDir temp_dir_;
-  FilePath file_name_;  // Database filename.
-  scoped_refptr<RefCountedBytes> google_thumbnail_;
-  scoped_refptr<RefCountedBytes> random_thumbnail_;
-  scoped_refptr<RefCountedBytes> weewar_thumbnail_;
-  MessageLoop message_loop_;
-  CancelableRequestConsumer consumer_;
+  // Waits for top sites to finish processing a task. This is useful if you need
+  // to wait until top sites finishes processing a task.
+  void WaitForTopSites() {
+    top_sites()->backend_->DoEmptyRequest(
+        &consumer_,
+        NewCallback(this, &TopSitesTest::QuitCallback));
+    MessageLoop::current()->Run();
+  }
 
-  DISALLOW_COPY_AND_ASSIGN(TopSitesTest);
-};
+  TopSites* top_sites() { return profile_->GetTopSites(); }
+  CancelableRequestConsumer* consumer() { return &consumer_; }
+  TestingProfile* profile() {return profile_.get();}
+  HistoryService* history_service() {
+    return profile_->GetHistoryService(Profile::EXPLICIT_ACCESS);
+  }
+
+  MostVisitedURLList GetPrepopulatePages() {
+    return TopSites::GetPrepopulatePages();
+  }
 
+  // Returns true if the TopSitesQuerier contains the prepopulate data starting
+  // at |start_index|.
+  void ContainsPrepopulatePages(const TopSitesQuerier& querier,
+                                size_t start_index) {
+    MostVisitedURLList prepopulate_urls = GetPrepopulatePages();
+    ASSERT_LE(start_index + prepopulate_urls.size(), querier.urls().size());
+    for (size_t i = 0; i < prepopulate_urls.size(); ++i) {
+      EXPECT_EQ(prepopulate_urls[i].url.spec(),
+                querier.urls()[start_index + i].url.spec()) << " @ index " <<
+          i;
+    }
+  }
 
-// A mockup of a HistoryService used for testing TopSites.
-class MockHistoryServiceImpl : public TopSites::MockHistoryService {
- public:
-  MockHistoryServiceImpl() : num_thumbnail_requests_(0) {}
-
-  // Calls the callback directly with the results.
-  HistoryService::Handle QueryMostVisitedURLs(
-      int result_count, int days_back,
-      CancelableRequestConsumerBase* consumer,
-      HistoryService::QueryMostVisitedURLsCallback* callback) {
-    callback->Run(CancelableRequestProvider::Handle(0),  // Handle is unused.
-                  most_visited_urls_);
-    delete callback;
-    return 0;
+  // Used for callbacks from history.
+  void EmptyCallback() {
   }
 
-  // Add a page to the end of the pages list.
-  void AppendMockPage(const GURL& url,
-                      const string16& title) {
-    MostVisitedURL page;
-    page.url = url;
-    page.title = title;
-    page.redirects = RedirectList();
-    page.redirects.push_back(url);
-    most_visited_urls_.push_back(page);
+  // Quit the current message loop when invoked. Useful when running a nested
+  // message loop.
+  void QuitCallback(TopSitesBackend::Handle handle) {
+    MessageLoop::current()->Quit();
   }
 
-  // Removes the last URL in the list.
-  void RemoveMostVisitedURL() {
-    most_visited_urls_.pop_back();
+  // Adds a page to history.
+  void AddPageToHistory(const GURL& url) {
+    RedirectList redirects;
+    redirects.push_back(url);
+    history_service()->AddPage(
+        url, static_cast<void*>(this), 0, GURL(), PageTransition::TYPED,
+        redirects, history::SOURCE_BROWSED, false);
   }
 
-  virtual void GetPageThumbnail(
-      const GURL& url,
-      CancelableRequestConsumerTSimple<size_t>* consumer,
-      HistoryService::ThumbnailDataCallback* callback,
-      size_t index) {
-    num_thumbnail_requests_++;
-    MostVisitedURL mvu;
-    mvu.url = url;
-    MostVisitedURLList::iterator pos = std::find(most_visited_urls_.begin(),
-                                                 most_visited_urls_.end(),
-                                                 mvu);
-    EXPECT_TRUE(pos != most_visited_urls_.end()) << url.spec();
-    scoped_refptr<RefCountedBytes> thumbnail;
-    callback->Run(index, thumbnail);
-    delete callback;
+  // Adds a page to history.
+  void AddPageToHistory(const GURL& url, const string16& title) {
+    RedirectList redirects;
+    redirects.push_back(url);
+    history_service()->AddPage(
+        url, static_cast<void*>(this), 0, GURL(), PageTransition::TYPED,
+        redirects, history::SOURCE_BROWSED, false);
+    history_service()->SetPageTitle(url, title);
   }
 
-  void ResetNumberOfThumbnailRequests() {
-    num_thumbnail_requests_ = 0;
+  // Adds a page to history.
+  void AddPageToHistory(const GURL& url,
+                        const string16& title,
+                        const history::RedirectList& redirects,
+                        base::Time time) {
+    history_service()->AddPage(
+        url, time, static_cast<void*>(this), 0, GURL(), PageTransition::TYPED,
+        redirects, history::SOURCE_BROWSED, false);
+    history_service()->SetPageTitle(url, title);
   }
 
-  int GetNumberOfThumbnailRequests() {
-    return num_thumbnail_requests_;
+  // Delets a url.
+  void DeleteURL(const GURL& url) {
+    history_service()->DeleteURL(url);
   }
 
- private:
-  MostVisitedURLList most_visited_urls_;
-  int num_thumbnail_requests_;  // Number of calls to GetPageThumbnail.
-};
+  // Returns true if the thumbnail equals the specified bytes.
+  bool ThumbnailEqualsBytes(const SkBitmap& image, RefCountedBytes* bytes) {
+    scoped_refptr<RefCountedBytes> encoded_image;
+    EncodeBitmap(image, &encoded_image);
+    return ThumbnailsAreEqual(encoded_image, bytes);
+  }
 
+  // Recreates top sites. This forces top sites to reread from the db.
+  void RecreateTopSitesAndBlock() {
+    // Recreate TopSites and wait for it to load.
+    profile()->CreateTopSites();
+    // As history already loaded we have to fake this call.
+    profile()->BlockUntilTopSitesLoaded();
+  }
 
-// A mockup of a TopSitesDatabase used for testing TopSites.
-class MockTopSitesDatabaseImpl : public TopSitesDatabase {
- public:
-  virtual void GetPageThumbnails(MostVisitedURLList* urls,
-                                 std::map<GURL, Images>* thumbnails) {
-    // Return a copy of the vector.
-    *urls = top_sites_list_;
-    *thumbnails = thumbnails_map_;
+  // Wrappers that allow private TopSites functions to be called from the
+  // individual tests without making them all be friends.
+  GURL GetCanonicalURL(const GURL& url) {
+    return top_sites()->cache_->GetCanonicalURL(url);
   }
 
-  virtual void SetPageThumbnail(const MostVisitedURL& url, int url_rank,
-                                const Images& thumbnail) {
-    SetPageRank(url, url_rank);
-    // Update thubmnail
-    thumbnails_map_[url.url] = thumbnail;
+  void SetTopSites(const MostVisitedURLList& new_top_sites) {
+    top_sites()->SetTopSites(new_top_sites);
   }
 
-  virtual void UpdatePageRank(const MostVisitedURL& url, int new_rank) {
-    MostVisitedURLList::iterator pos = std::find(top_sites_list_.begin(),
-                                                 top_sites_list_.end(),
-                                                 url);
-    // Is it in the right position?
-    int rank = pos - top_sites_list_.begin();
-    if (rank != new_rank) {
-      // Move the URL to a new position.
-      top_sites_list_.erase(pos);
-      top_sites_list_.insert(top_sites_list_.begin() + new_rank, url);
-    }
+  void StartQueryForMostVisited() {
+    top_sites()->StartQueryForMostVisited();
   }
 
-  virtual void SetPageRank(const MostVisitedURL& url, int url_rank) {
-    // Check if this url is in the list, and at which position.
-    MostVisitedURLList::iterator pos = std::find(top_sites_list_.begin(),
-                                                 top_sites_list_.end(),
-                                                 url);
-    if (pos == top_sites_list_.end()) {
-      // Add it to the list.
-      top_sites_list_.insert(top_sites_list_.begin() + url_rank, url);
-    } else {
-      UpdatePageRank(url, url_rank);
-    }
+  bool EncodeBitmap(const SkBitmap& image,
+                    scoped_refptr<RefCountedBytes>* bytes) {
+    return TopSites::EncodeBitmap(image, bytes);
+  }
+
+  void SetLastNumUrlsChanged(size_t value) {
+    top_sites()->last_num_urls_changed_ = value;
   }
 
-  // Get a thumbnail for a given page. Returns true iff we have the thumbnail.
-  virtual bool GetPageThumbnail(const GURL& url,
-                                Images* thumbnail) {
-    std::map<GURL, Images>::const_iterator found =
-        thumbnails_map_.find(url);
-    if (found == thumbnails_map_.end())
-      return false;  // No thumbnail for this URL.
+  size_t last_num_urls_changed() { return top_sites()->last_num_urls_changed_; }
 
-    thumbnail->thumbnail = found->second.thumbnail;
-    thumbnail->thumbnail_score = found->second.thumbnail_score;
-    return true;
+  base::TimeDelta GetUpdateDelay() {
+    return top_sites()->GetUpdateDelay();
   }
 
-  virtual bool RemoveURL(const MostVisitedURL& url) {
-    // Comparison by url.
-    MostVisitedURLList::iterator pos = std::find(top_sites_list_.begin(),
-                                                 top_sites_list_.end(),
-                                                 url);
-    if (pos == top_sites_list_.end()) {
-      return false;
-    }
-    top_sites_list_.erase(pos);
-    thumbnails_map_.erase(url.url);
-    return true;
+  bool IsTopSitesLoaded() { return top_sites()->loaded_; }
+
+  bool AddPrepopulatedPages(MostVisitedURLList* urls) {
+    return TopSites::AddPrepopulatedPages(urls);
   }
 
  private:
-  MostVisitedURLList top_sites_list_;  // Keeps the URLs sorted by score (rank).
-  std::map<GURL, Images> thumbnails_map_;
-};
+  MessageLoopForUI message_loop_;
+  BrowserThread ui_thread_;
+  BrowserThread db_thread_;
+  scoped_ptr<TestingProfile> profile_;
+  CancelableRequestConsumer consumer_;
+  CommandLine original_command_line_;
+
+  DISALLOW_COPY_AND_ASSIGN(TopSitesTest);
+};  // Class TopSitesTest
 
+class TopSitesMigrationTest : public TopSitesTest {
+ public:
+  TopSitesMigrationTest() {}
+
+  virtual void SetUp() {
+    TopSitesTest::SetUp();
+
+    FilePath data_path;
+    ASSERT_TRUE(PathService::Get(chrome::DIR_TEST_DATA, &data_path));
+    data_path = data_path.AppendASCII("top_sites");
+
+    // Set up history and thumbnails as they would be before migration.
+    ASSERT_NO_FATAL_FAILURE(
+        ExecuteSQL(data_path.AppendASCII("history.19.sql"),
+                   profile()->GetPath().Append(chrome::kHistoryFilename)));
+    ASSERT_NO_FATAL_FAILURE(
+        ExecuteSQL(data_path.AppendASCII("thumbnails.3.sql"),
+                   profile()->GetPath().Append(chrome::kThumbnailsFilename)));
+
+    profile()->CreateHistoryService(false, false);
+    profile()->CreateTopSites();
+    profile()->BlockUntilTopSitesLoaded();
+  }
+
+  // Returns true if history and top sites should be created in SetUp.
+  virtual bool CreateHistoryAndTopSites() {
+    return false;
+  }
+
+ protected:
+  // Assertions for the migration test. This is extracted into a standalone
+  // method so that it can be invoked twice.
+  void MigrationAssertions() {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
+
+    // We shouldn't have gotten a callback.
+    EXPECT_EQ(1, querier.number_of_callbacks());
+
+    // The data we loaded should contain google and yahoo.
+    ASSERT_EQ(2u + GetPrepopulatePages().size(), querier.urls().size());
+    EXPECT_EQ(GURL("http://google.com/"), querier.urls()[0].url);
+    EXPECT_EQ(GURL("http://yahoo.com/"), querier.urls()[1].url);
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier, 2));
+
+    SkBitmap goog_thumbnail = GetThumbnail(GURL("http://google.com/"));
+    EXPECT_EQ(1, goog_thumbnail.width());
+
+    SkBitmap yahoo_thumbnail = GetThumbnail(GURL("http://yahoo.com/"));
+    EXPECT_EQ(2, yahoo_thumbnail.width());
+
+    // Favicon assertions are handled in ThumbnailDatabase.
+  }
+
+ private:
+  // Executes the sql from the file |sql_path| in the database at |db_path|.
+  void ExecuteSQL(const FilePath& sql_path,
+                  const FilePath& db_path) {
+    std::string sql;
+    ASSERT_TRUE(file_util::ReadFileToString(sql_path, &sql));
+    sql::Connection connection;
+    ASSERT_TRUE(connection.Open(db_path));
+    ASSERT_TRUE(connection.Execute(sql.c_str()));
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(TopSitesMigrationTest);
+};
 
 // Helper function for appending a URL to a vector of "most visited" URLs,
 // using the default values for everything but the URL.
@@ -276,18 +400,6 @@ static void AppendMostVisitedURL(std::vector<MostVisitedURL>* list,
   list->push_back(mv);
 }
 
-// Returns true if t1 and t2 contain the same data.
-static bool ThumbnailsAreEqual(RefCountedBytes* t1,
-                               RefCountedBytes* t2) {
-  if (!t1 || !t2)
-    return false;
-  if (t1->data.size() != t2->data.size())
-    return false;
-  return std::equal(t1->data.begin(),
-                    t1->data.end(),
-                    t2->data.begin());
-}
-
 // Same as AppendMostVisitedURL except that it adds a redirect from the first
 // URL to the second.
 static void AppendMostVisitedURLWithRedirect(
@@ -300,8 +412,8 @@ static void AppendMostVisitedURLWithRedirect(
   list->push_back(mv);
 }
 
+// Tests GetCanonicalURL.
 TEST_F(TopSitesTest, GetCanonicalURL) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
   // Have two chains:
   //   google.com -> www.google.com
   //   news.google.com (no redirects)
@@ -312,7 +424,7 @@ TEST_F(TopSitesTest, GetCanonicalURL) {
   std::vector<MostVisitedURL> most_visited;
   AppendMostVisitedURLWithRedirect(&most_visited, source, dest);
   AppendMostVisitedURL(&most_visited, news);
-  StoreMostVisited(&most_visited);
+  SetTopSites(most_visited);
 
   // Random URLs not in the database are returned unchanged.
   GURL result = GetCanonicalURL(GURL("http://fark.com/"));
@@ -331,6 +443,7 @@ TEST_F(TopSitesTest, GetCanonicalURL) {
   EXPECT_EQ(dest, result);
 }
 
+// Tests DiffMostVisited.
 TEST_F(TopSitesTest, DiffMostVisited) {
   GURL stays_the_same("http://staysthesame/");
   GURL gets_added_1("http://getsadded1/");
@@ -349,26 +462,25 @@ TEST_F(TopSitesTest, DiffMostVisited) {
   AppendMostVisitedURL(&new_list, gets_added_2);    // 2  (added)
   AppendMostVisitedURL(&new_list, gets_moved_1);    // 3  (moved from 2)
 
-  std::vector<size_t> added;
-  std::vector<size_t> deleted;
-  std::vector<size_t> moved;
-  DiffMostVisited(old_list, new_list, &added, &deleted, &moved);
+  history::TopSitesDelta delta;
+  history::TopSites::DiffMostVisited(old_list, new_list, &delta);
 
-  ASSERT_EQ(2u, added.size());
-  ASSERT_EQ(1u, deleted.size());
-  ASSERT_EQ(1u, moved.size());
+  ASSERT_EQ(2u, delta.added.size());
+  ASSERT_TRUE(gets_added_1 == delta.added[0].url.url);
+  ASSERT_EQ(1, delta.added[0].rank);
+  ASSERT_TRUE(gets_added_2 == delta.added[1].url.url);
+  ASSERT_EQ(2, delta.added[1].rank);
 
-  // There should be 2 URLs added, we don't assume what order they're in inside
-  // the result vector.
-  EXPECT_TRUE(added[0] == 1 || added[1] == 1);
-  EXPECT_TRUE(added[0] == 2 || added[1] == 2);
+  ASSERT_EQ(1u, delta.deleted.size());
+  ASSERT_TRUE(gets_deleted_1 == delta.deleted[0].url);
 
-  EXPECT_EQ(1u, deleted[0]);
-  EXPECT_EQ(3u, moved[0]);
+  ASSERT_EQ(1u, delta.moved.size());
+  ASSERT_TRUE(gets_moved_1 == delta.moved[0].url.url);
+  ASSERT_EQ(3, delta.moved[0].rank);
 }
 
+// Tests SetPageThumbnail.
 TEST_F(TopSitesTest, SetPageThumbnail) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
   GURL url1a("http://google.com/");
   GURL url1b("http://www.google.com/");
   GURL url2("http://images.google.com/");
@@ -384,13 +496,10 @@ TEST_F(TopSitesTest, SetPageThumbnail) {
   list.push_back(mv);
 
   // Save our most visited data containing that one site.
-  StoreMostVisited(&list);
+  SetTopSites(list);
 
   // Create a dummy thumbnail.
-  SkBitmap thumbnail;
-  thumbnail.setConfig(SkBitmap::kARGB_8888_Config, 4, 4);
-  thumbnail.allocPixels();
-  thumbnail.eraseRGB(0x00, 0x00, 0x00);
+  SkBitmap thumbnail(CreateBitmap(SK_ColorWHITE));
 
   base::Time now = base::Time::Now();
   ThumbnailScore low_score(1.0, true, true, now);
@@ -398,96 +507,117 @@ TEST_F(TopSitesTest, SetPageThumbnail) {
   ThumbnailScore high_score(0.0, true, true, now);
 
   // Setting the thumbnail for invalid pages should fail.
-  EXPECT_FALSE(top_sites().SetPageThumbnail(invalid_url,
-                                            thumbnail, medium_score));
+  EXPECT_FALSE(top_sites()->SetPageThumbnail(invalid_url,
+                                             thumbnail, medium_score));
 
   // Setting the thumbnail for url2 should succeed, lower scores shouldn't
   // replace it, higher scores should.
-  EXPECT_TRUE(top_sites().SetPageThumbnail(url2, thumbnail, medium_score));
-  EXPECT_FALSE(top_sites().SetPageThumbnail(url2, thumbnail, low_score));
-  EXPECT_TRUE(top_sites().SetPageThumbnail(url2, thumbnail, high_score));
+  EXPECT_TRUE(top_sites()->SetPageThumbnail(url2, thumbnail, medium_score));
+  EXPECT_FALSE(top_sites()->SetPageThumbnail(url2, thumbnail, low_score));
+  EXPECT_TRUE(top_sites()->SetPageThumbnail(url2, thumbnail, high_score));
 
   // Set on the redirect source should succeed. It should be replacable by
   // the same score on the redirect destination, which in turn should not
   // be replaced by the source again.
-  EXPECT_TRUE(top_sites().SetPageThumbnail(url1a, thumbnail, medium_score));
-  EXPECT_TRUE(top_sites().SetPageThumbnail(url1b, thumbnail, medium_score));
-  EXPECT_FALSE(top_sites().SetPageThumbnail(url1a, thumbnail, medium_score));
+  EXPECT_TRUE(top_sites()->SetPageThumbnail(url1a, thumbnail, medium_score));
+  EXPECT_TRUE(top_sites()->SetPageThumbnail(url1b, thumbnail, medium_score));
+  EXPECT_FALSE(top_sites()->SetPageThumbnail(url1a, thumbnail, medium_score));
+}
+
+// Makes sure a thumbnail is correctly removed when the page is removed.
+TEST_F(TopSitesTest, ThumbnailRemoved) {
+  GURL url("http://google.com/");
+
+  // Configure top sites with 'google.com'.
+  std::vector<MostVisitedURL> list;
+  AppendMostVisitedURL(&list, url);
+  SetTopSites(list);
+
+  // Create a dummy thumbnail.
+  SkBitmap thumbnail(CreateBitmap(SK_ColorRED));
+
+  base::Time now = base::Time::Now();
+  ThumbnailScore low_score(1.0, true, true, now);
+  ThumbnailScore medium_score(0.5, true, true, now);
+  ThumbnailScore high_score(0.0, true, true, now);
+
+  // Set the thumbnail.
+  EXPECT_TRUE(top_sites()->SetPageThumbnail(url, thumbnail, medium_score));
+
+  // Make sure the thumbnail was actually set.
+  scoped_refptr<RefCountedBytes> result;
+  EXPECT_TRUE(top_sites()->GetPageThumbnail(url, &result));
+  EXPECT_TRUE(ThumbnailEqualsBytes(thumbnail, result.get()));
+
+  // Reset the thumbnails and make sure we don't get it back.
+  SetTopSites(MostVisitedURLList());
+  EXPECT_FALSE(top_sites()->GetPageThumbnail(url, &result));
 }
 
+// Tests GetPageThumbnail.
 TEST_F(TopSitesTest, GetPageThumbnail) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
   MostVisitedURLList url_list;
-  MostVisitedURL url1(GURL("http://asdf.com"), GURL(), string16());
+  MostVisitedURL url1;
+  url1.url = GURL("http://asdf.com");
   url1.redirects.push_back(url1.url);
   url_list.push_back(url1);
 
-  MostVisitedURL url2(GURL("http://gmail.com"), GURL(), string16());
+  MostVisitedURL url2;
+  url2.url = GURL("http://gmail.com");
   url2.redirects.push_back(url2.url);
   url2.redirects.push_back(GURL("http://mail.google.com"));
   url_list.push_back(url2);
 
-  top_sites().UpdateMostVisited(url_list);
-  MessageLoop::current()->RunAllPending();
+  SetTopSites(url_list);
 
   // Create a dummy thumbnail.
-  SkBitmap thumbnail;
-  thumbnail.setConfig(SkBitmap::kARGB_8888_Config, 4, 4);
-  thumbnail.allocPixels();
-  thumbnail.eraseRGB(0x00, 0x00, 0x00);
+  SkBitmap thumbnail(CreateBitmap(SK_ColorWHITE));
   ThumbnailScore score(0.5, true, true, base::Time::Now());
 
-  RefCountedBytes* result = NULL;
-  EXPECT_TRUE(top_sites().SetPageThumbnail(url1.url, thumbnail, score));
-  EXPECT_TRUE(top_sites().GetPageThumbnail(url1.url, &result));
+  scoped_refptr<RefCountedBytes> result;
+  EXPECT_TRUE(top_sites()->SetPageThumbnail(url1.url, thumbnail, score));
+  EXPECT_TRUE(top_sites()->GetPageThumbnail(url1.url, &result));
 
-  EXPECT_TRUE(top_sites().SetPageThumbnail(GURL("http://gmail.com"),
+  EXPECT_TRUE(top_sites()->SetPageThumbnail(GURL("http://gmail.com"),
                                            thumbnail, score));
-  EXPECT_TRUE(top_sites().GetPageThumbnail(GURL("http://gmail.com"),
-                                           &result));
+  EXPECT_TRUE(top_sites()->GetPageThumbnail(GURL("http://gmail.com"),
+                                            &result));
   // Get a thumbnail via a redirect.
-  EXPECT_TRUE(top_sites().GetPageThumbnail(GURL("http://mail.google.com"),
-                                           &result));
+  EXPECT_TRUE(top_sites()->GetPageThumbnail(GURL("http://mail.google.com"),
+                                            &result));
 
-  EXPECT_TRUE(top_sites().SetPageThumbnail(GURL("http://mail.google.com"),
+  EXPECT_TRUE(top_sites()->SetPageThumbnail(GURL("http://mail.google.com"),
                                            thumbnail, score));
-  EXPECT_TRUE(top_sites().GetPageThumbnail(url2.url, &result));
+  EXPECT_TRUE(top_sites()->GetPageThumbnail(url2.url, &result));
 
-  scoped_ptr<SkBitmap> out_bitmap(gfx::JPEGCodec::Decode(result->front(),
-                                                         result->size()));
-  EXPECT_EQ(0, memcmp(thumbnail.getPixels(), out_bitmap->getPixels(),
-                      thumbnail.getSize()));
+  EXPECT_TRUE(ThumbnailEqualsBytes(thumbnail, result.get()));
 }
 
+// Tests GetMostVisitedURLs.
 TEST_F(TopSitesTest, GetMostVisited) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
   GURL news("http://news.google.com/");
   GURL google("http://google.com/");
 
-  MockHistoryServiceImpl hs;
-  hs.AppendMockPage(news, ASCIIToUTF16("Google News"));
-  hs.AppendMockPage(google, ASCIIToUTF16("Google"));
-  top_sites().SetMockHistoryService(&hs);
-
-  top_sites().StartQueryForMostVisited();
-  MessageLoop::current()->RunAllPending();
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
+  AddPageToHistory(news);
+  AddPageToHistory(google);
+
+  StartQueryForMostVisited();
+  WaitForHistory();
+
+  TopSitesQuerier querier;
+  querier.QueryTopSites(top_sites(), false);
+
+  ASSERT_EQ(1, querier.number_of_callbacks());
+
   // 2 extra prepopulated URLs.
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ(news, urls()[0].url);
-  EXPECT_EQ(google, urls()[1].url);
-  EXPECT_EQ(welcome_url(), urls()[2].url);
-  EXPECT_EQ(themes_url(), urls()[3].url);
+  ASSERT_EQ(2u + GetPrepopulatePages().size(), querier.urls().size());
+  EXPECT_EQ(news, querier.urls()[0].url);
+  EXPECT_EQ(google, querier.urls()[1].url);
+  ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier, 2));
 }
 
-TEST_F(TopSitesTest, MockDatabase) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
-  MockTopSitesDatabaseImpl* db = new MockTopSitesDatabaseImpl;
-  // |db| is destroyed when the top_sites is destroyed in TearDown.
-  top_sites().db_.reset(db);
+// Makes sure changes done to top sites get mirrored to the db.
+TEST_F(TopSitesTest, SaveToDB) {
   MostVisitedURL url;
   GURL asdf_url("http://asdf.com");
   string16 asdf_title(ASCIIToUTF16("ASDF"));
@@ -496,155 +626,62 @@ TEST_F(TopSitesTest, MockDatabase) {
   GURL news_url("http://news.google.com");
   string16 news_title(ASCIIToUTF16("Google News"));
 
-  url.url = asdf_url;
-  url.title = asdf_title;
-  url.redirects.push_back(url.url);
-  Images thumbnail;
-  db->SetPageThumbnail(url, 0, thumbnail);
+  // Add asdf_url to history.
+  AddPageToHistory(asdf_url, asdf_title);
+
+  // Make TopSites reread from the db.
+  StartQueryForMostVisited();
+  WaitForHistory();
 
-  top_sites().ReadDatabase();
+  // Add a thumbnail.
+  SkBitmap tmp_bitmap(CreateBitmap(SK_ColorBLUE));
+  ASSERT_TRUE(top_sites()->SetPageThumbnail(asdf_url, tmp_bitmap,
+                                            ThumbnailScore()));
 
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  ASSERT_EQ(3u, urls().size());
-  EXPECT_EQ(asdf_url, urls()[0].url);
-  EXPECT_EQ(asdf_title, urls()[0].title);
-  EXPECT_EQ(welcome_url(), urls()[1].url);
-  EXPECT_EQ(themes_url(), urls()[2].url);
+  RecreateTopSitesAndBlock();
+
+  {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
+    ASSERT_EQ(1u + GetPrepopulatePages().size(), querier.urls().size());
+    EXPECT_EQ(asdf_url, querier.urls()[0].url);
+    EXPECT_EQ(asdf_title, querier.urls()[0].title);
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier, 1));
+
+    scoped_refptr<RefCountedBytes> read_data;
+    EXPECT_TRUE(top_sites()->GetPageThumbnail(asdf_url, &read_data));
+    EXPECT_TRUE(ThumbnailEqualsBytes(tmp_bitmap, read_data.get()));
+  }
 
   MostVisitedURL url2;
   url2.url = google_url;
   url2.title = google_title;
   url2.redirects.push_back(url2.url);
 
-  // Add new thumbnail at rank 0 and shift the other result to 1.
-  db->SetPageThumbnail(url2, 0, thumbnail);
-
-  top_sites().ReadDatabase();
-
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ(google_url, urls()[0].url);
-  EXPECT_EQ(google_title, urls()[0].title);
-  EXPECT_EQ(asdf_url, urls()[1].url);
-  EXPECT_EQ(asdf_title, urls()[1].title);
-  EXPECT_EQ(welcome_url(), urls()[2].url);
-  EXPECT_EQ(themes_url(), urls()[3].url);
-
-  MockHistoryServiceImpl hs;
-  // Add one old, one new URL to the history.
-  hs.AppendMockPage(google_url, google_title);
-  hs.AppendMockPage(news_url, news_title);
-  top_sites().SetMockHistoryService(&hs);
-
-  // This writes the new data to the DB.
-  top_sites().StartQueryForMostVisited();
-  MessageLoop::current()->RunAllPending();
-
-  std::map<GURL, Images> thumbnails;
-  MostVisitedURLList result;
-  db->GetPageThumbnails(&result, &thumbnails);
-  ASSERT_EQ(4u, result.size());
-  EXPECT_EQ(google_title, result[0].title);
-  EXPECT_EQ(news_title, result[1].title);
-}
-
-// Test TopSitesDatabaseImpl.
-TEST_F(TopSitesTest, TopSitesDB) {
-  TopSitesDatabaseImpl db;
+  AddPageToHistory(url2.url, url2.title);
 
-  ASSERT_TRUE(db.Init(file_name()));
+  // Add new thumbnail at rank 0 and shift the other result to 1.
+  ASSERT_TRUE(top_sites()->SetPageThumbnail(google_url,
+                                            tmp_bitmap,
+                                            ThumbnailScore()));
 
-  MostVisitedURL url;
-  GURL asdf_url("http://asdf.com");
-  string16 asdf_title(ASCIIToUTF16("ASDF"));
-  GURL google_url("http://google.com");
-  string16 google_title(ASCIIToUTF16("Google"));
-  GURL news_url("http://news.google.com");
-  string16 news_title(ASCIIToUTF16("Google News"));
+  // Make TopSites reread from the db.
+  RefreshTopSitesAndRecreate();
 
-  url.url = asdf_url;
-  url.title = asdf_title;
-  url.redirects.push_back(url.url);
-  Images thumbnail;
-  thumbnail.thumbnail = random_thumbnail();
-  // Add asdf at rank 0.
-  db.SetPageThumbnail(url, 0, thumbnail);
-
-  Images result;
-  EXPECT_TRUE(db.GetPageThumbnail(url.url, &result));
-  EXPECT_EQ(thumbnail.thumbnail->data.size(), result.thumbnail->data.size());
-  EXPECT_TRUE(ThumbnailsAreEqual(thumbnail.thumbnail, result.thumbnail));
-
-  MostVisitedURLList urls;
-  std::map<GURL, Images> thumbnails;
-  db.GetPageThumbnails(&urls, &thumbnails);
-  ASSERT_EQ(1u, urls.size());
-  EXPECT_EQ(asdf_url, urls[0].url);
-  EXPECT_EQ(asdf_title, urls[0].title);
-
-  url.url = google_url;
-  url.title = google_title;
-
-  // Add google at rank 1 - no rank shifting.
-  db.SetPageThumbnail(url, 1, thumbnail);
-  db.GetPageThumbnails(&urls, &thumbnails);
-  ASSERT_EQ(2u, urls.size());
-  EXPECT_EQ(asdf_url, urls[0].url);
-  EXPECT_EQ(asdf_title, urls[0].title);
-  EXPECT_EQ(google_url, urls[1].url);
-  EXPECT_EQ(google_title, urls[1].title);
-
-  url.url = news_url;
-  url.title = news_title;
-
-  // Add news at rank 1 - shift google to rank 2.
-  db.SetPageThumbnail(url, 1, thumbnail);
-  db.GetPageThumbnails(&urls, &thumbnails);
-  ASSERT_EQ(3u, urls.size());
-  EXPECT_EQ(asdf_url, urls[0].url);
-  EXPECT_EQ(news_url, urls[1].url);
-  EXPECT_EQ(google_url, urls[2].url);
-
-  // Move news at rank 0 - shift the rest up.
-  db.SetPageThumbnail(url, 0, thumbnail);
-  db.GetPageThumbnails(&urls, &thumbnails);
-  ASSERT_EQ(3u, urls.size());
-  EXPECT_EQ(news_url, urls[0].url);
-  EXPECT_EQ(asdf_url, urls[1].url);
-  EXPECT_EQ(google_url, urls[2].url);
-
-  // Move news at rank 2 - shift the rest down.
-  db.SetPageThumbnail(url, 2, thumbnail);
-  db.GetPageThumbnails(&urls, &thumbnails);
-  ASSERT_EQ(3u, urls.size());
-  EXPECT_EQ(asdf_url, urls[0].url);
-  EXPECT_EQ(google_url, urls[1].url);
-  EXPECT_EQ(news_url, urls[2].url);
-
-  // Delete asdf.
-  url.url = asdf_url;
-  db.RemoveURL(url);
-
-  db.GetPageThumbnails(&urls, &thumbnails);
-  ASSERT_EQ(2u, urls.size());
-  EXPECT_EQ(google_url, urls[0].url);
-  EXPECT_EQ(news_url, urls[1].url);
+  {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
+    ASSERT_EQ(2u + GetPrepopulatePages().size(), querier.urls().size());
+    EXPECT_EQ(asdf_url, querier.urls()[0].url);
+    EXPECT_EQ(asdf_title, querier.urls()[0].title);
+    EXPECT_EQ(google_url, querier.urls()[1].url);
+    EXPECT_EQ(google_title, querier.urls()[1].title);
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier, 2));
+  }
 }
 
-// Test TopSites with a real database.
+// More permutations of saving to db.
 TEST_F(TopSitesTest, RealDatabase) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
-  TopSitesDatabaseImpl* db = new TopSitesDatabaseImpl;
-
-  ASSERT_TRUE(db->Init(file_name()));
-  // |db| is destroyed when the top_sites is destroyed in TearDown.
-  top_sites().db_.reset(db);
   MostVisitedURL url;
   GURL asdf_url("http://asdf.com");
   string16 asdf_title(ASCIIToUTF16("ASDF"));
@@ -658,130 +695,106 @@ TEST_F(TopSitesTest, RealDatabase) {
   url.url = asdf_url;
   url.title = asdf_title;
   url.redirects.push_back(url.url);
-  Images thumbnail;
-  thumbnail.thumbnail = random_thumbnail();
-  db->SetPageThumbnail(url, 0, thumbnail);
-
-  top_sites().ReadDatabase();
-
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  ASSERT_EQ(3u, urls().size());
-  EXPECT_EQ(asdf_url, urls()[0].url);
-  EXPECT_EQ(asdf_title, urls()[0].title);
-  EXPECT_EQ(welcome_url(), urls()[1].url);
-  EXPECT_EQ(themes_url(), urls()[2].url);
-
-  Images img_result;
-  db->GetPageThumbnail(asdf_url, &img_result);
-  EXPECT_TRUE(img_result.thumbnail != NULL);
-  EXPECT_TRUE(ThumbnailsAreEqual(random_thumbnail(), img_result.thumbnail));
-
-  RefCountedBytes* thumbnail_result;
-  EXPECT_TRUE(top_sites().GetPageThumbnail(asdf_url, &thumbnail_result));
-  EXPECT_TRUE(thumbnail_result != NULL);
-  EXPECT_TRUE(ThumbnailsAreEqual(random_thumbnail(), thumbnail_result));
+  SkBitmap asdf_thumbnail(CreateBitmap(SK_ColorRED));
+  ASSERT_TRUE(top_sites()->SetPageThumbnail(
+                  asdf_url, asdf_thumbnail, ThumbnailScore()));
+
+  base::Time add_time(base::Time::Now());
+  AddPageToHistory(url.url, url.title, url.redirects, add_time);
+
+  RefreshTopSitesAndRecreate();
+
+  {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
+
+    ASSERT_EQ(1u + GetPrepopulatePages().size(), querier.urls().size());
+    EXPECT_EQ(asdf_url, querier.urls()[0].url);
+    EXPECT_EQ(asdf_title, querier.urls()[0].title);
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier, 1));
+
+    scoped_refptr<RefCountedBytes> read_data;
+    EXPECT_TRUE(top_sites()->GetPageThumbnail(asdf_url, &read_data));
+    EXPECT_TRUE(ThumbnailEqualsBytes(asdf_thumbnail, read_data.get()));
+  }
 
   MostVisitedURL url2;
-  url2.url = google1_url;
+  url2.url = google3_url;
   url2.title = google_title;
   url2.redirects.push_back(google1_url);
   url2.redirects.push_back(google2_url);
   url2.redirects.push_back(google3_url);
 
-  // Add new thumbnail at rank 0 and shift the other result to 1.
-  Images g_thumbnail;
-  g_thumbnail.thumbnail = google_thumbnail();
-  db->SetPageThumbnail(url2, 0, g_thumbnail);
-
-  top_sites().ReadDatabase();
-
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ(google1_url, urls()[0].url);
-  EXPECT_EQ(google_title, urls()[0].title);
-  EXPECT_TRUE(top_sites().GetPageThumbnail(google1_url, &thumbnail_result));
-  EXPECT_TRUE(ThumbnailsAreEqual(google_thumbnail(), thumbnail_result));
-  ASSERT_EQ(3u, urls()[0].redirects.size());
-  EXPECT_EQ(google1_url, urls()[0].redirects[0]);
-  EXPECT_EQ(google2_url, urls()[0].redirects[1]);
-  EXPECT_EQ(google3_url, urls()[0].redirects[2]);
-
-  EXPECT_EQ(asdf_url, urls()[1].url);
-  EXPECT_EQ(asdf_title, urls()[1].title);
-  EXPECT_EQ(welcome_url(), urls()[2].url);
-  EXPECT_EQ(themes_url(), urls()[3].url);
-
-  MockHistoryServiceImpl hs;
-  // Add one old, one new URL to the history.
-  hs.AppendMockPage(google1_url, google_title);
-  hs.AppendMockPage(news_url, news_title);
-  top_sites().SetMockHistoryService(&hs);
-
-  // This requests data from History Service and  writes it to the DB.
-  top_sites().StartQueryForMostVisited();
-  MessageLoop::current()->RunAllPending();
-
-  std::map<GURL, Images> thumbnails;
-  MostVisitedURLList results;
-  db->GetPageThumbnails(&results, &thumbnails);
-  ASSERT_EQ(4u, results.size());
-  EXPECT_EQ(google_title, results[0].title);
-  EXPECT_EQ(news_title, results[1].title);
-
-  scoped_ptr<SkBitmap> weewar_bitmap(
-      gfx::JPEGCodec::Decode(weewar_thumbnail()->front(),
-                             weewar_thumbnail()->size()));
+  AddPageToHistory(google3_url, url2.title, url2.redirects,
+                   add_time - base::TimeDelta::FromMinutes(1));
+  // Add google twice so that it becomes the first visited site.
+  AddPageToHistory(google3_url, url2.title, url2.redirects,
+                   add_time - base::TimeDelta::FromMinutes(2));
 
-  base::Time now = base::Time::Now();
-  ThumbnailScore low_score(1.0, true, true, now);
-  ThumbnailScore medium_score(0.5, true, true, now);
-  ThumbnailScore high_score(0.0, true, true, now);
+  SkBitmap google_thumbnail(CreateBitmap(SK_ColorBLUE));
+  ASSERT_TRUE(top_sites()->SetPageThumbnail(
+                  url2.url, google_thumbnail, ThumbnailScore()));
 
-  // 1. Set to weewar. (Writes the thumbnail to the DB.)
-  EXPECT_TRUE(top_sites().SetPageThumbnail(google1_url,
-                                           *weewar_bitmap,
-                                           medium_score));
-  RefCountedBytes* out_1;
-  Images out_2;
-  EXPECT_TRUE(top_sites().GetPageThumbnail(google1_url, &out_1));
+  RefreshTopSitesAndRecreate();
 
-  MessageLoop::current()->RunAllPending();
+  {
+    scoped_refptr<RefCountedBytes> read_data;
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
+
+    ASSERT_EQ(2u + GetPrepopulatePages().size(), querier.urls().size());
+    EXPECT_EQ(google1_url, querier.urls()[0].url);
+    EXPECT_EQ(google_title, querier.urls()[0].title);
+    ASSERT_EQ(3u, querier.urls()[0].redirects.size());
+    EXPECT_TRUE(top_sites()->GetPageThumbnail(google3_url, &read_data));
+    EXPECT_TRUE(ThumbnailEqualsBytes(google_thumbnail, read_data.get()));
+
+    EXPECT_EQ(asdf_url, querier.urls()[1].url);
+    EXPECT_EQ(asdf_title, querier.urls()[1].title);
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier, 2));
+  }
 
-  db->GetPageThumbnail(url2.url, &out_2);
-  EXPECT_TRUE(ThumbnailsAreEqual(out_1, out_2.thumbnail));
+  SkBitmap weewar_bitmap(CreateBitmap(SK_ColorYELLOW));
 
-  scoped_ptr<SkBitmap> google_bitmap(
-      gfx::JPEGCodec::Decode(google_thumbnail()->front(),
-                             google_thumbnail()->size()));
+  base::Time thumbnail_time(base::Time::Now());
+  ThumbnailScore low_score(1.0, true, true, thumbnail_time);
+  ThumbnailScore medium_score(0.5, true, true, thumbnail_time);
+  ThumbnailScore high_score(0.0, true, true, thumbnail_time);
+
+  // 1. Set to weewar. (Writes the thumbnail to the DB.)
+  EXPECT_TRUE(top_sites()->SetPageThumbnail(google3_url,
+                                            weewar_bitmap,
+                                            medium_score));
+  RefreshTopSitesAndRecreate();
+  {
+    scoped_refptr<RefCountedBytes> read_data;
+    EXPECT_TRUE(top_sites()->GetPageThumbnail(google3_url, &read_data));
+    EXPECT_TRUE(ThumbnailEqualsBytes(weewar_bitmap, read_data.get()));
+  }
+
+  SkBitmap google_bitmap(CreateBitmap(SK_ColorGREEN));
 
   // 2. Set to google - low score.
-  EXPECT_FALSE(top_sites().SetPageThumbnail(google1_url,
-                                            *google_bitmap,
-                                            low_score));
+  EXPECT_FALSE(top_sites()->SetPageThumbnail(google3_url,
+                                             google_bitmap,
+                                             low_score));
 
   // 3. Set to google - high score.
-  EXPECT_TRUE(top_sites().SetPageThumbnail(google1_url,
-                                           *google_bitmap,
-                                           high_score));
+  EXPECT_TRUE(top_sites()->SetPageThumbnail(google1_url,
+                                            google_bitmap,
+                                            high_score));
+
   // Check that the thumbnail was updated.
-  EXPECT_TRUE(top_sites().GetPageThumbnail(google1_url, &out_1));
-  EXPECT_FALSE(ThumbnailsAreEqual(out_1, out_2.thumbnail));
-  MessageLoop::current()->RunAllPending();
-
-  // Read the new thumbnail from the DB - should match what's in TopSites.
-  db->GetPageThumbnail(url2.url, &out_2);
-  EXPECT_TRUE(ThumbnailsAreEqual(out_1, out_2.thumbnail));
-  EXPECT_TRUE(high_score.Equals(out_2.thumbnail_score));
+  RefreshTopSitesAndRecreate();
+  {
+    scoped_refptr<RefCountedBytes> read_data;
+    EXPECT_TRUE(top_sites()->GetPageThumbnail(google3_url, &read_data));
+    EXPECT_FALSE(ThumbnailEqualsBytes(weewar_bitmap, read_data.get()));
+    EXPECT_TRUE(ThumbnailEqualsBytes(google_bitmap, read_data.get()));
+  }
 }
 
 TEST_F(TopSitesTest, DeleteNotifications) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
   GURL google1_url("http://google.com");
   GURL google2_url("http://google.com/redirect");
   GURL google3_url("http://www.google.com");
@@ -789,61 +802,70 @@ TEST_F(TopSitesTest, DeleteNotifications) {
   GURL news_url("http://news.google.com");
   string16 news_title(ASCIIToUTF16("Google News"));
 
-  MockHistoryServiceImpl hs;
+  AddPageToHistory(google1_url, google_title);
+  AddPageToHistory(news_url, news_title);
 
-  top_sites().Init(file_name());
+  RefreshTopSitesAndRecreate();
 
-  hs.AppendMockPage(google1_url, google_title);
-  hs.AppendMockPage(news_url, news_title);
-  top_sites().SetMockHistoryService(&hs);
+  {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
 
-  top_sites().StartQueryForMostVisited();
-  MessageLoop::current()->RunAllPending();
+    ASSERT_EQ(4u, querier.urls().size());
+  }
 
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  // 2 extra prepopulated URLs.
-  ASSERT_EQ(4u, urls().size());
-
-  hs.RemoveMostVisitedURL();
-
-  history::URLsDeletedDetails history_details;
-  history_details.all_history = false;
-  Details<URLsDeletedDetails> details(&history_details);
-  top_sites().Observe(NotificationType::HISTORY_URLS_DELETED,
-                      Source<Profile> (&profile()),
-                      details);
-  MessageLoop::current()->RunAllPending();
-
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  ASSERT_EQ(3u, urls().size());
-  EXPECT_EQ(google_title, urls()[0].title);
-  EXPECT_EQ(welcome_url(), urls()[1].url);
-  EXPECT_EQ(themes_url(), urls()[2].url);
-
-  hs.RemoveMostVisitedURL();
-  history_details.all_history = true;
-  details = Details<HistoryDetails>(&history_details);
-  top_sites().Observe(NotificationType::HISTORY_URLS_DELETED,
-                      Source<Profile> (&profile()),
-                      details);
-  MessageLoop::current()->RunAllPending();
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  ASSERT_EQ(2u, urls().size());
-  EXPECT_EQ(welcome_url(), urls()[0].url);
-  EXPECT_EQ(themes_url(), urls()[1].url);
+  DeleteURL(news_url);
+
+  // Wait for history to process the deletion.
+  WaitForHistory();
+
+  {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
+
+    ASSERT_EQ(1u + GetPrepopulatePages().size(), querier.urls().size());
+    EXPECT_EQ(google_title, querier.urls()[0].title);
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier, 1));
+  }
+
+  // Now reload. This verifies topsites actually wrote the deletion to disk.
+  RefreshTopSitesAndRecreate();
+
+  {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
+
+    ASSERT_EQ(1u + GetPrepopulatePages().size(), querier.urls().size());
+    EXPECT_EQ(google_title, querier.urls()[0].title);
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier, 1));
+  }
+
+  DeleteURL(google1_url);
+
+  // Wait for history to process the deletion.
+  WaitForHistory();
+
+  {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
+
+    ASSERT_EQ(GetPrepopulatePages().size(), querier.urls().size());
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier, 0));
+  }
+
+  // Now reload. This verifies topsites actually wrote the deletion to disk.
+  RefreshTopSitesAndRecreate();
+
+  {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
+
+    ASSERT_EQ(GetPrepopulatePages().size(), querier.urls().size());
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier, 0));
+  }
 }
 
 TEST_F(TopSitesTest, PinnedURLsDeleted) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
   GURL google1_url("http://google.com");
   GURL google2_url("http://google.com/redirect");
   GURL google3_url("http://www.google.com");
@@ -851,132 +873,130 @@ TEST_F(TopSitesTest, PinnedURLsDeleted) {
   GURL news_url("http://news.google.com");
   string16 news_title(ASCIIToUTF16("Google News"));
 
-  MockHistoryServiceImpl hs;
+  AddPageToHistory(google1_url, google_title);
+  AddPageToHistory(news_url, news_title);
+
+  RefreshTopSitesAndRecreate();
 
-  top_sites().Init(file_name());
+  {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
 
-  hs.AppendMockPage(google1_url, google_title);
-  hs.AppendMockPage(news_url, news_title);
-  top_sites().SetMockHistoryService(&hs);
+    // 2 extra prepopulated URLs.
+    ASSERT_EQ(4u, querier.urls().size());
+  }
 
-  top_sites().StartQueryForMostVisited();
-  MessageLoop::current()->RunAllPending();
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  MessageLoop::current()->RunAllPending();
-  EXPECT_EQ(1u, number_of_callbacks());
-  // 2 extra prepopulated URLs.
-  ASSERT_EQ(4u, urls().size());
-
-  top_sites().AddPinnedURL(news_url, 3);
-  EXPECT_TRUE(top_sites().IsURLPinned(news_url));
-
-  hs.RemoveMostVisitedURL();
-  history::URLsDeletedDetails history_details;
-  history_details.all_history = false;
-  history_details.urls.insert(news_url);
-  Details<URLsDeletedDetails> details(&history_details);
-  top_sites().Observe(NotificationType::HISTORY_URLS_DELETED,
-                      Source<Profile> (&profile()),
-                      details);
-  MessageLoop::current()->RunAllPending();
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  MessageLoop::current()->RunAllPending();
-  EXPECT_EQ(2u, number_of_callbacks());
-  ASSERT_EQ(3u, urls().size());
-  EXPECT_FALSE(top_sites().IsURLPinned(news_url));
-
-  hs.RemoveMostVisitedURL();
-  history_details.all_history = true;
-  details = Details<HistoryDetails>(&history_details);
-  top_sites().Observe(NotificationType::HISTORY_URLS_DELETED,
-                      Source<Profile> (&profile()),
-                      details);
-  MessageLoop::current()->RunAllPending();
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  ASSERT_EQ(2u, urls().size());
-  MessageLoop::current()->RunAllPending();
-
-  top_sites().StartQueryForMostVisited();
-  MessageLoop::current()->RunAllPending();
-  top_sites().GetMostVisitedURLs(
-      consumer(),
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  ASSERT_EQ(2u, urls().size());
-  EXPECT_EQ(welcome_url(), urls()[0].url);
-  EXPECT_EQ(themes_url(), urls()[1].url);
+  top_sites()->AddPinnedURL(news_url, 3);
+  EXPECT_TRUE(top_sites()->IsURLPinned(news_url));
+
+  DeleteURL(news_url);
+  WaitForHistory();
+
+  {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
+
+    // 2 extra prepopulated URLs.
+    ASSERT_EQ(3u, querier.urls().size());
+    EXPECT_FALSE(top_sites()->IsURLPinned(news_url));
+  }
+
+  history_service()->ExpireHistoryBetween(
+      std::set<GURL>(), base::Time(), base::Time(),
+      consumer(), NewCallback(static_cast<TopSitesTest*>(this),
+                              &TopSitesTest::EmptyCallback)),
+  WaitForHistory();
+
+  {
+    TopSitesQuerier querier;
+    querier.QueryTopSites(top_sites(), false);
+
+    // 2 extra prepopulated URLs.
+    ASSERT_EQ(GetPrepopulatePages().size(), querier.urls().size());
+    EXPECT_FALSE(top_sites()->IsURLPinned(google1_url));
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier, 0));
+  }
 }
 
+// Makes sure GetUpdateDelay is updated appropriately.
 TEST_F(TopSitesTest, GetUpdateDelay) {
-  top_sites().last_num_urls_changed_ = 0;
-  EXPECT_EQ(30, top_sites().GetUpdateDelay().InSeconds());
+  SetLastNumUrlsChanged(0);
+  EXPECT_EQ(30, GetUpdateDelay().InSeconds());
 
-  top_sites().top_sites_.resize(20);
-  top_sites().last_num_urls_changed_ = 0;
-  EXPECT_EQ(60, top_sites().GetUpdateDelay().InMinutes());
+  MostVisitedURLList url_list;
+  url_list.resize(20);
+  GURL tmp_url(GURL("http://x"));
+  for (size_t i = 0; i < url_list.size(); ++i) {
+    url_list[i].url = tmp_url;
+    url_list[i].redirects.push_back(tmp_url);
+  }
+  SetTopSites(url_list);
+  EXPECT_EQ(20u, last_num_urls_changed());
+  SetLastNumUrlsChanged(0);
+  EXPECT_EQ(60, GetUpdateDelay().InMinutes());
 
-  top_sites().last_num_urls_changed_ = 3;
-  EXPECT_EQ(52, top_sites().GetUpdateDelay().InMinutes());
+  SetLastNumUrlsChanged(3);
+  EXPECT_EQ(52, GetUpdateDelay().InMinutes());
 
-  top_sites().last_num_urls_changed_ = 20;
-  EXPECT_EQ(1, top_sites().GetUpdateDelay().InMinutes());
+  SetLastNumUrlsChanged(20);
+  EXPECT_EQ(1, GetUpdateDelay().InMinutes());
 }
 
-TEST_F(TopSitesTest, Migration) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
-  GURL google1_url("http://google.com");
-  string16 google_title(ASCIIToUTF16("Google"));
-  GURL news_url("http://news.google.com");
-  string16 news_title(ASCIIToUTF16("Google News"));
+TEST_F(TopSitesMigrationTest, Migrate) {
+  EXPECT_TRUE(IsTopSitesLoaded());
 
-  MockHistoryServiceImpl hs;
+  // Make sure the data was migrated to top sites.
+  ASSERT_NO_FATAL_FAILURE(MigrationAssertions());
 
-  top_sites().Init(file_name());
+  // We need to wait for top sites and history to finish processing requests.
+  WaitForTopSites();
+  WaitForHistory();
 
-  hs.AppendMockPage(google1_url, google_title);
-  hs.AppendMockPage(news_url, news_title);
-  top_sites().SetMockHistoryService(&hs);
-  MessageLoop::current()->RunAllPending();
+  // Make sure there is no longer a Thumbnails file on disk.
+  ASSERT_FALSE(file_util::PathExists(
+                   profile()->GetPath().Append(chrome::kThumbnailsFilename)));
 
-  top_sites().StartMigration();
-  EXPECT_TRUE(top_sites().migration_in_progress_);
-  MessageLoop::current()->RunAllPending();
-  EXPECT_EQ(2, hs.GetNumberOfThumbnailRequests());
-  EXPECT_FALSE(top_sites().migration_in_progress_);
+  // Recreate top sites and make sure everything is still there.
+  profile()->CreateHistoryService(false, false);
+  RecreateTopSitesAndBlock();
+
+  ASSERT_NO_FATAL_FAILURE(MigrationAssertions());
 }
 
-TEST_F(TopSitesTest, QueueingRequestsForTopSites) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
-  CancelableRequestConsumer c1;
-  CancelableRequestConsumer c2;
-  CancelableRequestConsumer c3;
-  top_sites().GetMostVisitedURLs(
-      &c1,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-
-  top_sites().GetMostVisitedURLs(
-      &c2,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-
-  top_sites().GetMostVisitedURLs(
-      &c3,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-
-  EXPECT_EQ(0u, number_of_callbacks());
-  EXPECT_EQ(0u, urls().size());
+// Verifies that callbacks are notified correctly if requested before top sites
+// has loaded.
+TEST_F(TopSitesTest, NotifyCallbacksWhenLoaded) {
+  // Recreate top sites. It won't be loaded now.
+  profile()->CreateTopSites();
+
+  EXPECT_FALSE(IsTopSitesLoaded());
+
+  TopSitesQuerier querier1;
+  TopSitesQuerier querier2;
+  TopSitesQuerier querier3;
+
+  // Starts the queries.
+  querier1.QueryTopSites(top_sites(), false);
+  querier2.QueryTopSites(top_sites(), false);
+  querier3.QueryTopSites(top_sites(), false);
+
+  // We shouldn't have gotten a callback.
+  EXPECT_EQ(0, querier1.number_of_callbacks());
+  EXPECT_EQ(0, querier2.number_of_callbacks());
+  EXPECT_EQ(0, querier3.number_of_callbacks());
 
+  // Wait for loading to complete.
+  profile()->BlockUntilTopSitesLoaded();
+
+  // Now we should have gotten the callbacks.
+  EXPECT_EQ(1, querier1.number_of_callbacks());
+  EXPECT_EQ(GetPrepopulatePages().size(), querier1.urls().size());
+  EXPECT_EQ(1, querier2.number_of_callbacks());
+  EXPECT_EQ(GetPrepopulatePages().size(), querier2.urls().size());
+  EXPECT_EQ(1, querier3.number_of_callbacks());
+  EXPECT_EQ(GetPrepopulatePages().size(), querier3.urls().size());
+
+  // Reset the top sites.
   MostVisitedURLList pages;
   MostVisitedURL url;
   url.url = GURL("http://1.com/");
@@ -985,109 +1005,107 @@ TEST_F(TopSitesTest, QueueingRequestsForTopSites) {
   url.url = GURL("http://2.com/");
   url.redirects.push_back(url.url);
   pages.push_back(url);
-  top_sites().OnTopSitesAvailable(0, pages);
-  MessageLoop::current()->RunAllPending();
+  SetTopSites(pages);
+
+  // Recreate top sites. It won't be loaded now.
+  profile()->CreateTopSites();
+
+  EXPECT_FALSE(IsTopSitesLoaded());
 
-  EXPECT_EQ(3u, number_of_callbacks());
+  TopSitesQuerier querier4;
 
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ("http://1.com/", urls()[0].url.spec());
-  EXPECT_EQ("http://2.com/", urls()[1].url.spec());
-  EXPECT_EQ(welcome_url(), urls()[2].url);
-  EXPECT_EQ(themes_url(), urls()[3].url);
+  // Query again.
+  querier4.QueryTopSites(top_sites(), false);
 
+  // We shouldn't have gotten a callback.
+  EXPECT_EQ(0, querier4.number_of_callbacks());
 
+  // Wait for loading to complete.
+  profile()->BlockUntilTopSitesLoaded();
+
+  // Now we should have gotten the callbacks.
+  EXPECT_EQ(1, querier4.number_of_callbacks());
+  ASSERT_EQ(2u + GetPrepopulatePages().size(), querier4.urls().size());
+
+  EXPECT_EQ("http://1.com/", querier4.urls()[0].url.spec());
+  EXPECT_EQ("http://2.com/", querier4.urls()[1].url.spec());
+  ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier4, 2));
+
+  // Reset the top sites again, this time don't reload.
   url.url = GURL("http://3.com/");
   url.redirects.push_back(url.url);
   pages.push_back(url);
-  top_sites().OnTopSitesAvailable(0, pages);
-  MessageLoop::current()->RunAllPending();
+  SetTopSites(pages);
 
-  top_sites().GetMostVisitedURLs(
-      &c3,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
+  // Query again.
+  TopSitesQuerier querier5;
+  querier5.QueryTopSites(top_sites(), true);
 
-  EXPECT_EQ(4u, number_of_callbacks());
-
-  ASSERT_EQ(5u, urls().size());
-  EXPECT_EQ("http://1.com/", urls()[0].url.spec());
-  EXPECT_EQ("http://2.com/", urls()[1].url.spec());
-  EXPECT_EQ("http://3.com/", urls()[2].url.spec());
-  EXPECT_EQ(welcome_url(), urls()[3].url);
-  EXPECT_EQ(themes_url(), urls()[4].url);
+  EXPECT_EQ(1, querier5.number_of_callbacks());
 
+  ASSERT_EQ(3u + GetPrepopulatePages().size(), querier5.urls().size());
+  EXPECT_EQ("http://1.com/", querier5.urls()[0].url.spec());
+  EXPECT_EQ("http://2.com/", querier5.urls()[1].url.spec());
+  EXPECT_EQ("http://3.com/", querier5.urls()[2].url.spec());
+  ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(querier5, 3));
 }
 
+// Makes sure canceled requests are not notified.
 TEST_F(TopSitesTest, CancelingRequestsForTopSites) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
-  CancelableRequestConsumer c1;
-  CancelableRequestConsumer c2;
-  top_sites().GetMostVisitedURLs(
-      &c1,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-
-  top_sites().GetMostVisitedURLs(
-      &c2,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
+  // Recreate top sites. It won't be loaded now.
+  profile()->CreateTopSites();
 
-  {
-    CancelableRequestConsumer c3;
-    top_sites().GetMostVisitedURLs(
-        &c3,
-        NewCallback(static_cast<TopSitesTest*>(this),
-                    &TopSitesTest::OnTopSitesAvailable));
-    // c3 is out of scope, and the request should be cancelled.
-  }
+  EXPECT_FALSE(IsTopSitesLoaded());
 
-  // No requests until OnTopSitesAvailable is called.
-  EXPECT_EQ(0u, number_of_callbacks());
-  EXPECT_EQ(0u, urls().size());
+  TopSitesQuerier querier1;
+  TopSitesQuerier querier2;
 
-  MostVisitedURLList pages;
-  MostVisitedURL url;
-  url.url = GURL("http://1.com/");
-  url.redirects.push_back(url.url);
-  pages.push_back(url);
-  url.url = GURL("http://2.com/");
-  pages.push_back(url);
+  // Starts the queries.
+  querier1.QueryTopSites(top_sites(), false);
+  querier2.QueryTopSites(top_sites(), false);
 
-  top_sites().OnTopSitesAvailable(0, pages);
-  MessageLoop::current()->RunAllPending();
+  // We shouldn't have gotten a callback.
+  EXPECT_EQ(0, querier1.number_of_callbacks());
+  EXPECT_EQ(0, querier2.number_of_callbacks());
 
-  // 1 request was canceled.
-  EXPECT_EQ(2u, number_of_callbacks());
+  querier2.CancelRequest();
 
-  // 2 extra prepopulated URLs.
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ("http://1.com/", urls()[0].url.spec());
-  EXPECT_EQ("http://2.com/", urls()[1].url.spec());
+  // Wait for loading to complete.
+  profile()->BlockUntilTopSitesLoaded();
+
+  // The first callback should succeed.
+  EXPECT_EQ(1, querier1.number_of_callbacks());
+  EXPECT_EQ(GetPrepopulatePages().size(), querier1.urls().size());
+
+  // And the canceled callback should not be notified.
+  EXPECT_EQ(0, querier2.number_of_callbacks());
 }
 
+// Makes sure temporary thumbnails are copied over correctly.
 TEST_F(TopSitesTest, AddTemporaryThumbnail) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
   GURL unknown_url("http://news.google.com/");
   GURL invalid_url("chrome://thumb/http://google.com/");
   GURL url1a("http://google.com/");
   GURL url1b("http://www.google.com/");
 
   // Create a dummy thumbnail.
-  SkBitmap thumbnail;
-  thumbnail.setConfig(SkBitmap::kARGB_8888_Config, 4, 4);
-  thumbnail.allocPixels();
-  thumbnail.eraseRGB(0x00, 0x00, 0x00);
+  SkBitmap thumbnail(CreateBitmap(SK_ColorRED));
 
   ThumbnailScore medium_score(0.5, true, true, base::Time::Now());
 
   // Don't store thumbnails for Javascript URLs.
-  EXPECT_FALSE(top_sites().SetPageThumbnail(invalid_url,
-                                            thumbnail, medium_score));
+  EXPECT_FALSE(top_sites()->SetPageThumbnail(invalid_url,
+                                             thumbnail,
+                                             medium_score));
   // Store thumbnails for unknown (but valid) URLs temporarily - calls
   // AddTemporaryThumbnail.
-  EXPECT_TRUE(top_sites().SetPageThumbnail(unknown_url,
-                                           thumbnail, medium_score));
+  EXPECT_TRUE(top_sites()->SetPageThumbnail(unknown_url,
+                                            thumbnail,
+                                            medium_score));
+
+  // We shouldn't get the thumnail back though (the url isn't in to sites yet).
+  scoped_refptr<RefCountedBytes> out;
+  EXPECT_FALSE(top_sites()->GetPageThumbnail(unknown_url, &out));
 
   std::vector<MostVisitedURL> list;
 
@@ -1098,19 +1116,15 @@ TEST_F(TopSitesTest, AddTemporaryThumbnail) {
   mv.redirects.push_back(url1b);
   list.push_back(mv);
 
-  // Update URLs - use temporary thumbnails.
-  top_sites().UpdateMostVisited(list);
+  // Update URLs. This should result in using thumbnail.
+  SetTopSites(list);
 
-  RefCountedBytes* out = NULL;
-  ASSERT_TRUE(top_sites().GetPageThumbnail(unknown_url, &out));
-  scoped_ptr<SkBitmap> out_bitmap(gfx::JPEGCodec::Decode(out->front(),
-                                                         out->size()));
-  EXPECT_EQ(0, memcmp(thumbnail.getPixels(), out_bitmap->getPixels(),
-                      thumbnail.getSize()));
+  ASSERT_TRUE(top_sites()->GetPageThumbnail(unknown_url, &out));
+  EXPECT_TRUE(ThumbnailEqualsBytes(thumbnail, out.get()));
 }
 
+// Tests variations of blacklisting.
 TEST_F(TopSitesTest, Blacklisting) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
   MostVisitedURLList pages;
   MostVisitedURL url, url1;
   url.url = GURL("http://bbc.com/");
@@ -1120,91 +1134,83 @@ TEST_F(TopSitesTest, Blacklisting) {
   url1.redirects.push_back(url1.url);
   pages.push_back(url1);
 
-  CancelableRequestConsumer c;
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  top_sites().OnTopSitesAvailable(0, pages);
-  MessageLoop::current()->RunAllPending();
+  SetTopSites(pages);
+  EXPECT_FALSE(top_sites()->IsBlacklisted(GURL("http://bbc.com/")));
+
+  // Blacklist google.com.
+  top_sites()->AddBlacklistedURL(GURL("http://google.com/"));
+
+  GURL prepopulate_url = GetPrepopulatePages()[0].url;
+
+  EXPECT_TRUE(top_sites()->HasBlacklistedItems());
+  EXPECT_TRUE(top_sites()->IsBlacklisted(GURL("http://google.com/")));
+  EXPECT_FALSE(top_sites()->IsBlacklisted(GURL("http://bbc.com/")));
+  EXPECT_FALSE(top_sites()->IsBlacklisted(prepopulate_url));
+
+  // Make sure the blacklisted site isn't returned in the results.
   {
-    Lock& l = lock();
-    AutoLock lock(l);  // IsBlacklisted must be in a lock.
-    EXPECT_FALSE(top_sites().IsBlacklisted(GURL("http://bbc.com/")));
+    TopSitesQuerier q;
+    q.QueryTopSites(top_sites(), true);
+    ASSERT_EQ(1u + GetPrepopulatePages().size(), q.urls().size());
+    EXPECT_EQ("http://bbc.com/", q.urls()[0].url.spec());
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(q, 1));
   }
 
-  EXPECT_EQ(1u, number_of_callbacks());
+  // Recreate top sites and make sure blacklisted url was correctly read.
+  RecreateTopSitesAndBlock();
+  {
+    TopSitesQuerier q;
+    q.QueryTopSites(top_sites(), true);
+    ASSERT_EQ(1u + GetPrepopulatePages().size(), q.urls().size());
+    EXPECT_EQ("http://bbc.com/", q.urls()[0].url.spec());
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(q, 1));
+  }
 
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ("http://bbc.com/", urls()[0].url.spec());
-  EXPECT_EQ("http://google.com/", urls()[1].url.spec());
-  EXPECT_EQ(welcome_url(), urls()[2].url);
-  EXPECT_EQ(themes_url(), urls()[3].url);
-  EXPECT_FALSE(top_sites().HasBlacklistedItems());
+  // Blacklist one of the prepopulate urls.
+  top_sites()->AddBlacklistedURL(prepopulate_url);
+  EXPECT_TRUE(top_sites()->HasBlacklistedItems());
 
-  top_sites().AddBlacklistedURL(GURL("http://google.com/"));
-  EXPECT_TRUE(top_sites().HasBlacklistedItems());
+  // Make sure the blacklisted prepopulate url isn't returned.
   {
-    Lock& l = lock();
-    AutoLock lock(l);  // IsBlacklisted must be in a lock.
-    EXPECT_TRUE(top_sites().IsBlacklisted(GURL("http://google.com/")));
-    EXPECT_FALSE(top_sites().IsBlacklisted(GURL("http://bbc.com/")));
-    EXPECT_FALSE(top_sites().IsBlacklisted(welcome_url()));
+    TopSitesQuerier q;
+    q.QueryTopSites(top_sites(), true);
+    ASSERT_EQ(1u + GetPrepopulatePages().size() - 1, q.urls().size());
+    EXPECT_EQ("http://bbc.com/", q.urls()[0].url.spec());
+    for (size_t i = 1; i < q.urls().size(); ++i)
+      EXPECT_NE(prepopulate_url.spec(), q.urls()[i].url.spec());
   }
 
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  MessageLoop::current()->RunAllPending();
-  EXPECT_EQ(2u, number_of_callbacks());
-  ASSERT_EQ(3u, urls().size());
-  EXPECT_EQ("http://bbc.com/", urls()[0].url.spec());
-  EXPECT_EQ(welcome_url(), urls()[1].url);
-  EXPECT_EQ(themes_url(), urls()[2].url);
-
-  top_sites().AddBlacklistedURL(welcome_url());
-  EXPECT_TRUE(top_sites().HasBlacklistedItems());
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  ASSERT_EQ(2u, urls().size());
-  EXPECT_EQ("http://bbc.com/", urls()[0].url.spec());
-  EXPECT_EQ(themes_url(), urls()[1].url);
-
-  top_sites().RemoveBlacklistedURL(GURL("http://google.com/"));
-  EXPECT_TRUE(top_sites().HasBlacklistedItems());
+  // Mark google as no longer blacklisted.
+  top_sites()->RemoveBlacklistedURL(GURL("http://google.com/"));
+  EXPECT_TRUE(top_sites()->HasBlacklistedItems());
+  EXPECT_FALSE(top_sites()->IsBlacklisted(GURL("http://google.com/")));
+
+  // Make sure google is returned now.
   {
-    Lock& l = lock();
-    AutoLock lock(l);  // IsBlacklisted must be in a lock.
-    EXPECT_FALSE(top_sites().IsBlacklisted(GURL("http://google.com/")));
+    TopSitesQuerier q;
+    q.QueryTopSites(top_sites(), true);
+    ASSERT_EQ(2u + GetPrepopulatePages().size() - 1, q.urls().size());
+    EXPECT_EQ("http://bbc.com/", q.urls()[0].url.spec());
+    EXPECT_EQ("http://google.com/", q.urls()[1].url.spec());
+    EXPECT_NE(prepopulate_url.spec(), q.urls()[2].url.spec());
   }
 
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  ASSERT_EQ(3u, urls().size());
-  EXPECT_EQ("http://bbc.com/", urls()[0].url.spec());
-  EXPECT_EQ("http://google.com/", urls()[1].url.spec());
-  EXPECT_EQ(themes_url(), urls()[2].url);
-
-  top_sites().ClearBlacklistedURLs();
-  EXPECT_FALSE(top_sites().HasBlacklistedItems());
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ("http://bbc.com/", urls()[0].url.spec());
-  EXPECT_EQ("http://google.com/", urls()[1].url.spec());
-  EXPECT_EQ(welcome_url(), urls()[2].url);
-  EXPECT_EQ(themes_url(), urls()[3].url);
+  // Remove all blacklisted sites.
+  top_sites()->ClearBlacklistedURLs();
+  EXPECT_FALSE(top_sites()->HasBlacklistedItems());
+
+  {
+    TopSitesQuerier q;
+    q.QueryTopSites(top_sites(), true);
+    ASSERT_EQ(2u + GetPrepopulatePages().size(), q.urls().size());
+    EXPECT_EQ("http://bbc.com/", q.urls()[0].url.spec());
+    EXPECT_EQ("http://google.com/", q.urls()[1].url.spec());
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(q, 2));
+  }
 }
 
+// Tests variations of pinning/unpinning urls.
 TEST_F(TopSitesTest, PinnedURLs) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
   MostVisitedURLList pages;
   MostVisitedURL url, url1;
   url.url = GURL("http://bbc.com/");
@@ -1214,127 +1220,127 @@ TEST_F(TopSitesTest, PinnedURLs) {
   url1.redirects.push_back(url1.url);
   pages.push_back(url1);
 
-  CancelableRequestConsumer c;
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  top_sites().OnTopSitesAvailable(0, pages);
-  MessageLoop::current()->RunAllPending();
-  EXPECT_FALSE(top_sites().IsURLPinned(GURL("http://bbc.com/")));
-
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ("http://bbc.com/", urls()[0].url.spec());
-  EXPECT_EQ("http://google.com/", urls()[1].url.spec());
-  EXPECT_EQ(welcome_url(), urls()[2].url);
-  EXPECT_EQ(themes_url(), urls()[3].url);
-
-  top_sites().AddPinnedURL(GURL("http://google.com/"), 3);
-  EXPECT_FALSE(top_sites().IsURLPinned(GURL("http://bbc.com/")));
-  EXPECT_FALSE(top_sites().IsURLPinned(welcome_url()));
-
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  EXPECT_EQ(2u, number_of_callbacks());
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ("http://bbc.com/", urls()[0].url.spec());
-  EXPECT_EQ(welcome_url(), urls()[1].url);
-  EXPECT_EQ(themes_url(), urls()[2].url);
-  EXPECT_EQ("http://google.com/", urls()[3].url.spec());
-
-  top_sites().RemovePinnedURL(GURL("http://google.com/"));
-  EXPECT_FALSE(top_sites().IsURLPinned(GURL("http://google.com/")));
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ("http://bbc.com/", urls()[0].url.spec());
-  EXPECT_EQ("http://google.com/", urls()[1].url.spec());
-  EXPECT_EQ(welcome_url(), urls()[2].url);
-  EXPECT_EQ(themes_url(), urls()[3].url);
-
-  top_sites().AddPinnedURL(GURL("http://bbc.com"), 1);
-  top_sites().AddPinnedURL(themes_url(), 0);
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ(themes_url(), urls()[0].url);
-  EXPECT_EQ("http://bbc.com/", urls()[1].url.spec());
-  EXPECT_EQ("http://google.com/", urls()[2].url.spec());
-  EXPECT_EQ(welcome_url(), urls()[3].url);
-
-  top_sites().RemovePinnedURL(GURL("http://bbc.com"));
-  top_sites().RemovePinnedURL(themes_url());
-
-  top_sites().AddPinnedURL(welcome_url(), 1);
-  top_sites().AddPinnedURL(GURL("http://bbc.com"), 3);
-
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-
-  ASSERT_EQ(4u, urls().size());
-  EXPECT_EQ("http://google.com/", urls()[0].url.spec());
-  EXPECT_EQ(welcome_url(), urls()[1].url);
-  EXPECT_EQ(themes_url(), urls()[2].url);
-  EXPECT_EQ("http://bbc.com/", urls()[3].url.spec());
+  SetTopSites(pages);
+
+  EXPECT_FALSE(top_sites()->IsURLPinned(GURL("http://bbc.com/")));
+
+  {
+    TopSitesQuerier q;
+    q.QueryTopSites(top_sites(), true);
+    ASSERT_EQ(2u + GetPrepopulatePages().size(), q.urls().size());
+    EXPECT_EQ("http://bbc.com/", q.urls()[0].url.spec());
+    EXPECT_EQ("http://google.com/", q.urls()[1].url.spec());
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(q, 2));
+  }
+
+  top_sites()->AddPinnedURL(GURL("http://google.com/"), 3);
+  EXPECT_FALSE(top_sites()->IsURLPinned(GURL("http://bbc.com/")));
+  EXPECT_FALSE(top_sites()->IsURLPinned(GetPrepopulatePages()[0].url));
+
+  {
+    TopSitesQuerier q;
+    q.QueryTopSites(top_sites(), true);
+    ASSERT_EQ(4u, q.urls().size());
+    EXPECT_EQ("http://bbc.com/", q.urls()[0].url.spec());
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(q, 1));
+    EXPECT_EQ("http://google.com/", q.urls()[3].url.spec());
+  }
+
+  top_sites()->RemovePinnedURL(GURL("http://google.com/"));
+  EXPECT_FALSE(top_sites()->IsURLPinned(GURL("http://google.com/")));
+  {
+    TopSitesQuerier q;
+    q.QueryTopSites(top_sites(), true);
+
+    ASSERT_EQ(2u + GetPrepopulatePages().size(), q.urls().size());
+    EXPECT_EQ("http://bbc.com/", q.urls()[0].url.spec());
+    EXPECT_EQ("http://google.com/", q.urls()[1].url.spec());
+    ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(q, 2));
+  }
+
+  GURL prepopulate_url = GetPrepopulatePages()[0].url;
+  top_sites()->AddPinnedURL(GURL("http://bbc.com"), 1);
+  top_sites()->AddPinnedURL(prepopulate_url, 0);
+  {
+    TopSitesQuerier q;
+    q.QueryTopSites(top_sites(), true);
+
+    ASSERT_EQ(3u + GetPrepopulatePages().size() - 1, q.urls().size());
+    EXPECT_EQ(prepopulate_url, q.urls()[0].url);
+    EXPECT_EQ("http://bbc.com/", q.urls()[1].url.spec());
+    EXPECT_EQ("http://google.com/", q.urls()[2].url.spec());
+    if (GetPrepopulatePages().size() > 1)
+      EXPECT_EQ(GetPrepopulatePages()[1].url, q.urls()[3].url);
+  }
+
+  // Recreate and make sure state remains the same.
+  RecreateTopSitesAndBlock();
+  {
+    TopSitesQuerier q;
+    q.QueryTopSites(top_sites(), true);
+
+    ASSERT_EQ(3u + GetPrepopulatePages().size() - 1, q.urls().size());
+    EXPECT_EQ(prepopulate_url, q.urls()[0].url);
+    EXPECT_EQ("http://bbc.com/", q.urls()[1].url.spec());
+    EXPECT_EQ("http://google.com/", q.urls()[2].url.spec());
+    if (GetPrepopulatePages().size() > 1)
+      EXPECT_EQ(GetPrepopulatePages()[1].url, q.urls()[3].url);
+  }
 }
 
+// Tests blacklisting and pinning.
 TEST_F(TopSitesTest, BlacklistingAndPinnedURLs) {
-  BrowserThread db_loop(BrowserThread::DB, MessageLoop::current());
-  MostVisitedURLList pages;
-  CancelableRequestConsumer c;
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-  top_sites().OnTopSitesAvailable(0, pages);
-  MessageLoop::current()->RunAllPending();
-
-  ASSERT_EQ(2u, urls().size());
-  EXPECT_EQ(welcome_url(), urls()[0].url);
-  EXPECT_EQ(themes_url(), urls()[1].url);
-
-  top_sites().AddPinnedURL(themes_url(), 1);
-  top_sites().AddBlacklistedURL(welcome_url());
-
-  top_sites().GetMostVisitedURLs(
-      &c,
-      NewCallback(static_cast<TopSitesTest*>(this),
-                  &TopSitesTest::OnTopSitesAvailable));
-
-  ASSERT_EQ(2u, urls().size());
-  EXPECT_EQ(GURL(), urls()[0].url);
-  EXPECT_EQ(themes_url(), urls()[1].url);
+  MostVisitedURLList prepopulate_urls = GetPrepopulatePages();
+  if (prepopulate_urls.size() < 2)
+    return;
+
+  top_sites()->AddPinnedURL(prepopulate_urls[0].url, 1);
+  top_sites()->AddBlacklistedURL(prepopulate_urls[1].url);
 
+  {
+    TopSitesQuerier q;
+    q.QueryTopSites(top_sites(), true);
+
+    ASSERT_LE(2u, q.urls().size());
+    EXPECT_EQ(GURL(), q.urls()[0].url);
+    EXPECT_EQ(prepopulate_urls[0].url, q.urls()[1].url);
+  }
 }
 
+// Makes sure prepopulated pages exist.
 TEST_F(TopSitesTest, AddPrepopulatedPages) {
-  MostVisitedURLList pages;
-  top_sites().AddPrepopulatedPages(&pages);
-  ASSERT_EQ(2u, pages.size());
-  EXPECT_EQ(welcome_url(), pages[0].url);
-  EXPECT_EQ(themes_url(), pages[1].url);
-
-  pages.clear();
+  TopSitesQuerier q;
+  q.QueryTopSites(top_sites(), true);
+  EXPECT_EQ(GetPrepopulatePages().size(), q.urls().size());
+  ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(q, 0));
 
-  MostVisitedURL url(themes_url(), GURL(), string16());
-  pages.push_back(url);
+  MostVisitedURLList pages = q.urls();
+  EXPECT_FALSE(AddPrepopulatedPages(&pages));
 
-  top_sites().AddPrepopulatedPages(&pages);
+  EXPECT_EQ(GetPrepopulatePages().size(), pages.size());
+  q.set_urls(pages);
+  ASSERT_NO_FATAL_FAILURE(ContainsPrepopulatePages(q, 0));
+}
 
-  // Themes URL is already in pages; should not be added twice.
-  ASSERT_EQ(2u, pages.size());
-  EXPECT_EQ(themes_url(), pages[0].url);
-  EXPECT_EQ(welcome_url(), pages[1].url);
+// Makes sure creating top sites before history is created works.
+TEST_F(TopSitesTest, CreateTopSitesThenHistory) {
+  profile()->DestroyTopSites();
+  profile()->DestroyHistoryService();
+
+  // Remove the TopSites file. This forces TopSites to wait until history loads
+  // before TopSites is considered loaded.
+  file_util::Delete(profile()->GetPath().Append(chrome::kTopSitesFilename),
+                    false);
+
+  // Create TopSites, but not History.
+  profile()->CreateTopSites();
+  WaitForTopSites();
+  EXPECT_FALSE(IsTopSitesLoaded());
+
+  // Load history, which should make TopSites finish loading too.
+  profile()->CreateHistoryService(false, false);
+  profile()->BlockUntilTopSitesLoaded();
+  EXPECT_TRUE(IsTopSitesLoaded());
 }
 
 }  // namespace history
diff --git a/chrome/browser/history/url_database.cc b/chrome/browser/history/url_database.cc
index b63d24a..3f297bd 100644
--- a/chrome/browser/history/url_database.cc
+++ b/chrome/browser/history/url_database.cc
@@ -247,16 +247,29 @@ bool URLDatabase::IsFavIconUsed(FavIconID favicon_id) {
 
 void URLDatabase::AutocompleteForPrefix(const string16& prefix,
                                         size_t max_results,
+                                        bool typed_only,
                                         std::vector<history::URLRow>* results) {
   // NOTE: this query originally sorted by starred as the second parameter. But
   // as bookmarks is no longer part of the db we no longer include the order
   // by clause.
   results->clear();
-  sql::Statement statement(GetDB().GetCachedStatement(SQL_FROM_HERE,
-      "SELECT" HISTORY_URL_ROW_FIELDS "FROM urls "
-      "WHERE url >= ? AND url < ? AND hidden = 0 "
-      "ORDER BY typed_count DESC, visit_count DESC, last_visit_time DESC "
-      "LIMIT ?"));
+  const char* sql;
+  int line;
+  if (typed_only) {
+    sql = "SELECT" HISTORY_URL_ROW_FIELDS "FROM urls "
+        "WHERE url >= ? AND url < ? AND hidden = 0 AND typed_count > 0 "
+        "ORDER BY typed_count DESC, visit_count DESC, last_visit_time DESC "
+        "LIMIT ?";
+    line = __LINE__;
+  } else {
+    sql = "SELECT" HISTORY_URL_ROW_FIELDS "FROM urls "
+        "WHERE url >= ? AND url < ? AND hidden = 0 "
+        "ORDER BY typed_count DESC, visit_count DESC, last_visit_time DESC "
+        "LIMIT ?";
+    line = __LINE__;
+  }
+  sql::Statement statement(
+      GetDB().GetCachedStatement(sql::StatementID(__FILE__, line), sql));
   if (!statement)
     return;
 
@@ -327,7 +340,10 @@ bool URLDatabase::InitKeywordSearchTermsTable() {
         "term LONGVARCHAR NOT NULL)"))      // The actual search term.
       return false;
   }
+  return true;
+}
 
+void URLDatabase::CreateKeywordSearchTermsIndices() {
   // For searching.
   GetDB().Execute("CREATE INDEX keyword_search_terms_index1 ON "
                   "keyword_search_terms (keyword_id, lower_term)");
@@ -335,8 +351,6 @@ bool URLDatabase::InitKeywordSearchTermsTable() {
   // For deletion.
   GetDB().Execute("CREATE INDEX keyword_search_terms_index2 ON "
                   "keyword_search_terms (url_id)");
-
-  return true;
 }
 
 bool URLDatabase::DropKeywordSearchTermsTable() {
diff --git a/chrome/browser/history/url_database.h b/chrome/browser/history/url_database.h
index 36bfebb..49bf5f0 100644
--- a/chrome/browser/history/url_database.h
+++ b/chrome/browser/history/url_database.h
@@ -138,10 +138,12 @@ class URLDatabase {
   // Autocomplete --------------------------------------------------------------
 
   // Fills the given array with URLs matching the given prefix. They will be
-  // sorted by typed count, then by visit count, then by visit date (most
-  // recent first) up to the given maximum number. Called by HistoryURLProvider.
+  // sorted by typed count, then by visit count, then by visit date (most recent
+  // first) up to the given maximum number.  If |typed_only| is true, only urls
+  // that have been typed once are returned. Called by HistoryURLProvider.
   void AutocompleteForPrefix(const string16& prefix,
                              size_t max_results,
+                             bool typed_only,
                              std::vector<URLRow>* results);
 
   // Tries to find the shortest URL beginning with |base| that strictly
@@ -218,6 +220,9 @@ class URLDatabase {
   // Ensures the keyword search terms table exists.
   bool InitKeywordSearchTermsTable();
 
+  // Creates the indices used for keyword search terms.
+  void CreateKeywordSearchTermsIndices();
+
   // Deletes the keyword search terms table.
   bool DropKeywordSearchTermsTable();
 
diff --git a/chrome/browser/history/url_database_unittest.cc b/chrome/browser/history/url_database_unittest.cc
index f567844..c37323f 100644
--- a/chrome/browser/history/url_database_unittest.cc
+++ b/chrome/browser/history/url_database_unittest.cc
@@ -52,6 +52,7 @@ class URLDatabaseTest : public testing::Test,
     CreateMainURLIndex();
     CreateSupplimentaryURLIndices();
     InitKeywordSearchTermsTable();
+    CreateKeywordSearchTermsIndices();
   }
   void TearDown() {
     db_.Close();