Make ThumbnailStore broadcast a notification when it has finished reading thumbnails from disk.

Make DOMUIThumbnailSource wait for this notification if ThumbnailStore isn't ready yet.
Also clean up some of the code.

Review URL: http://codereview.chromium.org/155911

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@21785 0039d316-1c4b-4281-b951-d872f2087c98

11 files changed, 207 insertions, 82 deletions

diff --git a/chrome/browser/dom_ui/dom_ui_thumbnail_source.cc b/chrome/browser/dom_ui/dom_ui_thumbnail_source.cc
index 5a10c7c..230389b 100644
--- a/chrome/browser/dom_ui/dom_ui_thumbnail_source.cc
+++ b/chrome/browser/dom_ui/dom_ui_thumbnail_source.cc
@@ -10,6 +10,7 @@
 #include "chrome/browser/profile.h"
 #include "chrome/browser/thumbnail_store.h"
 #include "chrome/common/chrome_switches.h"
+#include "chrome/common/notification_service.h"
 #include "chrome/common/url_constants.h"
 #include "googleurl/src/gurl.h"
 #include "grit/theme_resources.h"
@@ -23,20 +24,18 @@ DOMUIThumbnailSource::DOMUIThumbnailSource(Profile* profile)
 void DOMUIThumbnailSource::StartDataRequest(const std::string& path,
                                             int request_id) {
   if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kThumbnailStore)) {
-    RefCountedBytes* data = NULL;
     scoped_refptr<ThumbnailStore> store_ = profile_->GetThumbnailStore();
 
-    if (store_->GetPageThumbnail(GURL(path), &data)) {
-      // Got the thumbnail.
-      SendResponse(request_id, data);
-    } else {
-      // Don't have the thumbnail so return the default thumbnail.
-      if (!default_thumbnail_.get()) {
-        default_thumbnail_ = new RefCountedBytes;
-        ResourceBundle::GetSharedInstance().LoadImageResourceBytes(
-            IDR_DEFAULT_THUMBNAIL, &default_thumbnail_->data);
+    if (!store_->IsReady()) {
+      // Register to be notified when the ThumbnailStore is ready.
+      if (registrar_.IsEmpty()) {
+        registrar_.Add(this, NotificationType::THUMBNAIL_STORE_READY,
+            Source<ThumbnailStore>(store_.get()));
       }
-      SendResponse(request_id, default_thumbnail_);
+      // Insert into pending_requests.
+      pending_requests_.push_back(std::make_pair(path, request_id));
+    } else {
+      DoDataRequest(path, request_id);
     }
     return;
   }  // end --thumbnail-store switch
@@ -55,6 +54,24 @@ void DOMUIThumbnailSource::StartDataRequest(const std::string& path,
   }
 }
 
+void DOMUIThumbnailSource::DoDataRequest(const std::string& path,
+                                         int request_id) {
+  RefCountedBytes* data = NULL;
+  scoped_refptr<ThumbnailStore> store_ = profile_->GetThumbnailStore();
+  if (store_->GetPageThumbnail(GURL(path), &data)) {
+    // Got the thumbnail.
+    SendResponse(request_id, data);
+  } else {
+    // Don't have the thumbnail so return the default thumbnail.
+    if (!default_thumbnail_.get()) {
+      default_thumbnail_ = new RefCountedBytes;
+      ResourceBundle::GetSharedInstance().LoadImageResourceBytes(
+          IDR_DEFAULT_THUMBNAIL, &default_thumbnail_->data);
+    }
+    SendResponse(request_id, default_thumbnail_);
+  }
+}
+
 void DOMUIThumbnailSource::OnThumbnailDataAvailable(
     HistoryService::Handle request_handle,
     scoped_refptr<RefCountedBytes> data) {
@@ -74,3 +91,20 @@ void DOMUIThumbnailSource::OnThumbnailDataAvailable(
     SendResponse(request_id, default_thumbnail_);
   }
 }
+
+void DOMUIThumbnailSource::Observe(NotificationType type,
+                                   const NotificationSource& source,
+                                   const NotificationDetails& details) {
+  if (type.value != NotificationType::THUMBNAIL_STORE_READY) {
+    NOTREACHED();
+    return;
+  }
+
+  // This notification is sent only once.
+  registrar_.RemoveAll();
+
+  for (size_t i = 0; i < pending_requests_.size(); ++i)
+    DoDataRequest(pending_requests_[i].first, pending_requests_[i].second);
+
+  pending_requests_.clear();
+}
diff --git a/chrome/browser/dom_ui/dom_ui_thumbnail_source.h b/chrome/browser/dom_ui/dom_ui_thumbnail_source.h
index c94967b..4e1555d 100644
--- a/chrome/browser/dom_ui/dom_ui_thumbnail_source.h
+++ b/chrome/browser/dom_ui/dom_ui_thumbnail_source.h
@@ -5,20 +5,22 @@
 #ifndef CHROME_BROWSER_DOM_UI_DOM_UI_THUMBNAIL_SOURCE_H_
 #define CHROME_BROWSER_DOM_UI_DOM_UI_THUMBNAIL_SOURCE_H_
 
-#include <set>
 #include <string>
+#include <vector>
 
 #include "base/basictypes.h"
 #include "base/scoped_ptr.h"
 #include "chrome/browser/dom_ui/chrome_url_data_manager.h"
 #include "chrome/browser/history/history.h"
+#include "chrome/common/notification_registrar.h"
 
 class Profile;
 class ThumbnailStore;
 
 // ThumbnailSource is the gateway between network-level chrome:
 // requests for thumbnails and the history backend that serves these.
-class DOMUIThumbnailSource : public ChromeURLDataManager::DataSource {
+class DOMUIThumbnailSource : public ChromeURLDataManager::DataSource,
+                             public NotificationObserver {
  public:
   explicit DOMUIThumbnailSource(Profile* profile);
 
@@ -37,6 +39,14 @@ class DOMUIThumbnailSource : public ChromeURLDataManager::DataSource {
                                 scoped_refptr<RefCountedBytes> data);
 
  private:
+  // NotificationObserver implementation
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
+
+  // Fetch the specified resource.
+  void DoDataRequest(const std::string& path, int request_id);
+
   Profile* profile_;
   CancelableRequestConsumerT<int, 0> cancelable_consumer_;
 
@@ -44,6 +54,13 @@ class DOMUIThumbnailSource : public ChromeURLDataManager::DataSource {
   // database doesn't have a thumbnail for a webpage.
   scoped_refptr<RefCountedBytes> default_thumbnail_;
 
+  // Store requests when the ThumbnailStore isn't ready. When a notification is
+  // received that it is ready, then serve these requests.
+  std::vector<std::pair<std::string, int> > pending_requests_;
+
+  // To register to be notified when the ThumbnailStore is ready.
+  NotificationRegistrar registrar_;
+
   DISALLOW_COPY_AND_ASSIGN(DOMUIThumbnailSource);
 };
 
diff --git a/chrome/browser/history/history.h b/chrome/browser/history/history.h
index 9aec250..0643139 100644
--- a/chrome/browser/history/history.h
+++ b/chrome/browser/history/history.h
@@ -306,7 +306,10 @@ class HistoryService : public CancelableRequestProvider,
   // in the map containing redirects from the URL.  For example, if we have the
   // redirect chain A -> B -> C and A is a top visited URL, then A will be in
   // the vector and "A => {B -> C}" will be in the map.
-  typedef Callback2<std::vector<GURL>*, history::RedirectMap*>::Type
+  typedef Callback4<Handle,
+                    bool,  // Did we get the top urls and redirects?
+                    std::vector<GURL>*,  // List of top URLs.
+                    history::RedirectMap*>::Type  // Redirects for top URLs.
       QueryTopURLsAndRedirectsCallback;
 
   // Request the top |result_count| most visited URLs and the chain of redirects
diff --git a/chrome/browser/history/history_backend.cc b/chrome/browser/history/history_backend.cc
index bdf2351..1ccd7cf 100644
--- a/chrome/browser/history/history_backend.cc
+++ b/chrome/browser/history/history_backend.cc
@@ -1163,7 +1163,7 @@ void HistoryBackend::QueryTopURLsAndRedirects(
 
   if (!db_.get()) {
     request->ForwardResult(QueryTopURLsAndRedirectsRequest::TupleType(
-        NULL, NULL));
+        request->handle(), false, NULL, NULL));
     return;
   }
 
@@ -1176,13 +1176,13 @@ void HistoryBackend::QueryTopURLsAndRedirects(
 
   for (size_t i = 0; i < data.size(); ++i) {
     top_urls->push_back(data[i]->GetURL());
-    history::RedirectList list;
-    GetMostRecentRedirectsFrom(top_urls->back(), &list);
-    (*redirects)[top_urls->back()] = new RefCountedVector<GURL>(list);
+    RefCountedVector<GURL>* list = new RefCountedVector<GURL>;
+    GetMostRecentRedirectsFrom(top_urls->back(), &list->data);
+    (*redirects)[top_urls->back()] = list;
   }
 
   request->ForwardResult(QueryTopURLsAndRedirectsRequest::TupleType(
-      top_urls, redirects));
+      request->handle(), true, top_urls, redirects));
 }
 
 void HistoryBackend::GetRedirectsFromSpecificVisit(
diff --git a/chrome/browser/profile.cc b/chrome/browser/profile.cc
index f32a7bd..5d39188 100644
--- a/chrome/browser/profile.cc
+++ b/chrome/browser/profile.cc
@@ -1047,7 +1047,8 @@ TabRestoreService* ProfileImpl::GetTabRestoreService() {
 ThumbnailStore* ProfileImpl::GetThumbnailStore() {
   if (!thumbnail_store_.get()) {
     thumbnail_store_ = new ThumbnailStore;
-    thumbnail_store_->Init(GetPath().AppendASCII("Top Thumbnails"), this);
+    thumbnail_store_->Init(
+        GetPath().Append(chrome::kNewTabThumbnailsFilename), this);
   }
   return thumbnail_store_.get();
 }
diff --git a/chrome/browser/thumbnail_store.cc b/chrome/browser/thumbnail_store.cc
index e6f0e99..4f30c62 100644
--- a/chrome/browser/thumbnail_store.cc
+++ b/chrome/browser/thumbnail_store.cc
@@ -26,7 +26,8 @@ ThumbnailStore::ThumbnailStore()
     : cache_(NULL),
       db_(NULL),
       hs_(NULL),
-      url_blacklist_(NULL) {
+      url_blacklist_(NULL),
+      disk_data_loaded_(false) {
 }
 
 ThumbnailStore::~ThumbnailStore() {
@@ -34,8 +35,7 @@ ThumbnailStore::~ThumbnailStore() {
   DCHECK(hs_ == NULL);
 }
 
-void ThumbnailStore::Init(const FilePath& db_name,
-                          Profile* profile) {
+void ThumbnailStore::Init(const FilePath& db_name, Profile* profile) {
   // Load thumbnails already in the database.
   g_browser_process->file_thread()->message_loop()->PostTask(FROM_HERE,
       NewRunnableMethod(this, &ThumbnailStore::InitializeFromDB,
@@ -50,7 +50,9 @@ void ThumbnailStore::Init(const FilePath& db_name,
 
   // Get the list of most visited URLs and redirect information from the
   // HistoryService.
-  seconds_to_next_update_ = kInitialUpdateIntervalSecs;
+  most_visited_urls_.reset(new MostVisitedMap);
+  timer_.Start(base::TimeDelta::FromSeconds(kUpdateIntervalSecs), this,
+      &ThumbnailStore::UpdateURLData);
   UpdateURLData();
 
   // Register to get notified when the history is cleared.
@@ -139,8 +141,7 @@ void ThumbnailStore::Shutdown() {
   // for details.
   hs_ = NULL;
 
-  // The source of notifications is the Profile. We may outlive the Profile so
-  // we unregister for notifications here.
+  // De-register for notifications.
   registrar_.RemoveAll();
 
   // Stop the timer to ensure that UpdateURLData is not called during shutdown.
@@ -161,6 +162,11 @@ void ThumbnailStore::OnRedirectsForURLAvailable(
   if (!success)
     return;
 
+  DCHECK(redirect_urls_.get());
+
+  // If A -> B -> C is a redirect chain, then this function would be called
+  // with url=C and redirects = {B, A}. This is entered into the RedirectMap as
+  // A => {B -> C}.
   if (redirects->empty()) {
     (*redirect_urls_)[url] = new RefCountedVector<GURL>;
   } else {
@@ -171,9 +177,20 @@ void ThumbnailStore::OnRedirectsForURLAvailable(
   }
 }
 
+history::RedirectMap::iterator ThumbnailStore::GetRedirectIteratorForURL(
+    const GURL& url) const {
+  for (history::RedirectMap::iterator it = redirect_urls_->begin();
+      it != redirect_urls_->end(); ++it) {
+    if (it->first == url ||
+        (!it->second->data.empty() && it->second->data.back() == url))
+      return it;
+  }
+  return redirect_urls_->end();
+}
+
 void ThumbnailStore::Observe(NotificationType type,
-                             const NotificationSource& source,
-                             const NotificationDetails& details) {
+    const NotificationSource& source,
+    const NotificationDetails& details) {
   if (type.value != NotificationType::HISTORY_URLS_DELETED) {
     NOTREACHED();
     return;
@@ -183,37 +200,58 @@ void ThumbnailStore::Observe(NotificationType type,
   // If all history was cleared, clear all of our data and reset the update
   // timer.
   if (url_details->all_history) {
-    most_visited_urls_.reset();
-    redirect_urls_.reset();
-    cache_.reset();
-
-    timer_.Stop();
-    seconds_to_next_update_ = kInitialUpdateIntervalSecs;
-    timer_.Start(base::TimeDelta::FromSeconds(seconds_to_next_update_), this,
-        &ThumbnailStore::UpdateURLData);
+    most_visited_urls_->clear();
+    redirect_urls_->clear();
+    cache_->clear();
+    timer_.Reset();
   }
 }
 
+void ThumbnailStore::NotifyThumbnailStoreReady() {
+  NotificationService::current()->Notify(
+      NotificationType::THUMBNAIL_STORE_READY,
+      Source<ThumbnailStore>(this),
+      NotificationService::NoDetails());
+}
+
 void ThumbnailStore::UpdateURLData() {
+  DCHECK(url_blacklist_);
+
   int result_count = ThumbnailStore::kMaxCacheSize + url_blacklist_->GetSize();
   hs_->QueryTopURLsAndRedirects(result_count, &consumer_,
       NewCallback(this, &ThumbnailStore::OnURLDataAvailable));
 }
 
-void ThumbnailStore::OnURLDataAvailable(std::vector<GURL>* urls,
+void ThumbnailStore::OnURLDataAvailable(HistoryService::Handle handle,
+                                        bool success,
+                                        std::vector<GURL>* urls,
                                         history::RedirectMap* redirects) {
+  if (!success)
+    return;
+
   DCHECK(urls);
   DCHECK(redirects);
 
-  most_visited_urls_.reset(new std::vector<GURL>(*urls));
+  // Each element of |urls| is the start of a redirect chain. When thumbnails
+  // are stored from TabContents, the tails of the redirect chains are
+  // associated with the image. Since SetPageThumbnail is called frequently, we
+  // look up the tail end of each element in |urls| and insert that into the
+  // MostVisitedMap. This way SetPageThumbnail can more quickly check if a
+  // given url is in the most visited list.
+  most_visited_urls_->clear();
+  for (size_t i = 0; i < urls->size(); ++i) {
+    history::RedirectMap::iterator it = redirects->find(urls->at(i));
+    if (it->second->data.empty())
+      (*most_visited_urls_)[urls->at(i)] = GURL();
+    else
+      (*most_visited_urls_)[it->second->data.back()] = urls->at(i);
+  }
   redirect_urls_.reset(new history::RedirectMap(*redirects));
-  CleanCacheData();
 
-  // Schedule the next update.
-  if (seconds_to_next_update_ < kMaxUpdateIntervalSecs)
-    seconds_to_next_update_ *= 2;
-  timer_.Start(base::TimeDelta::FromSeconds(seconds_to_next_update_), this,
-      &ThumbnailStore::UpdateURLData);
+  if (IsReady())
+    NotifyThumbnailStoreReady();
+
+  CleanCacheData();
 }
 
 void ThumbnailStore::CleanCacheData() {
@@ -228,26 +266,15 @@ void ThumbnailStore::CleanCacheData() {
   // be written to disk.
   for (Cache::iterator cache_it = cache_->begin();
        cache_it != cache_->end();) {
-    const GURL* url = NULL;
-    // For each URL in the cache, search the RedirectMap for the originating
-    // URL.
-    for (history::RedirectMap::iterator it = redirect_urls_->begin();
-         it != redirect_urls_->end(); ++it) {
-      if (cache_it->first == it->first ||
-          (it->second->data.size() &&
-          cache_it->first == it->second->data.back())) {
-        url = &it->first;
-        break;
-      }
-    }
+    history::RedirectMap::iterator redirect_it =
+        GetRedirectIteratorForURL(cache_it->first);
+    const GURL* url = redirect_it == redirect_urls_->end() ?
+                          NULL : &redirect_it->first;
 
     // If this URL is blacklisted or not in the most visited list, mark it for
     // deletion. Otherwise, if the cache entry is dirty, mark it to be written
     // to disk.
     if (url == NULL || IsURLBlacklisted(*url) || !IsPopular(*url)) {
-      // Note that we don't check whether the cache entry is dirty or not. If
-      // it is not dirty, then the thumbnail exists on disk and must be
-      // deleted. If it is dirty, it may exist on disk so we delete it anyways.
       urls_to_delete->data.push_back(cache_it->first);
       cache_->erase(cache_it++);
     } else {
@@ -271,6 +298,8 @@ void ThumbnailStore::CommitCacheToDB(
   if (!db_)
     return;
 
+  base::TimeTicks db_start = base::TimeTicks::Now();
+
   int rv = sqlite3_exec(db_, "BEGIN TRANSACTION", NULL, NULL, NULL);
   DCHECK(rv == SQLITE_OK) << "Failed to begin transaction";
 
@@ -292,7 +321,8 @@ void ThumbnailStore::CommitCacheToDB(
          it != data_to_save->end(); ++it) {
       SQLITE_UNIQUE_STATEMENT(statement, *statement_cache_,
           "INSERT OR REPLACE INTO thumbnails "
-          "(url, boring_score, good_clipping, at_top, time_taken, data) "
+          "(url, boring_score, good_clipping, "
+          "at_top, time_taken, data) "
           "VALUES (?,?,?,?,?,?)");
       statement->bind_string(0, it->first.spec());
       statement->bind_double(1, it->second.score_.boring_score);
@@ -309,6 +339,9 @@ void ThumbnailStore::CommitCacheToDB(
 
   rv = sqlite3_exec(db_, "COMMIT", NULL, NULL, NULL);
   DCHECK(rv == SQLITE_OK) << "Failed to commit transaction";
+
+  base::TimeDelta delta = base::TimeTicks::Now() - db_start;
+  HISTOGRAM_TIMES("ThumbnailStore.WriteDBToDisk", delta);
 }
 
 void ThumbnailStore::InitializeFromDB(const FilePath& db_name,
@@ -351,18 +384,23 @@ void ThumbnailStore::InitializeFromDB(const FilePath& db_name,
 }
 
 void ThumbnailStore::GetAllThumbnailsFromDisk(MessageLoop* cb_loop) {
-  ThumbnailStore::Cache* cache = new ThumbnailStore::Cache;
+  Cache* cache = new Cache;
 
   SQLITE_UNIQUE_STATEMENT(statement, *statement_cache_,
       "SELECT * FROM thumbnails");
 
   while (statement->step() == SQLITE_ROW) {
+    // The URL
     GURL url(statement->column_string(0));
+
+    // The score.
     ThumbnailScore score(statement->column_double(1),      // Boring score
                          statement->column_bool(2),        // Good clipping
                          statement->column_bool(3),        // At top
                          base::Time::FromInternalValue(
                             statement->column_int64(4)));  // Time taken
+
+    // The image.
     scoped_refptr<RefCountedBytes> data = new RefCountedBytes;
     if (statement->column_blob_as_vector(5, &data->data))
       (*cache)[url] = CacheEntry(data, score, false);
@@ -372,17 +410,23 @@ void ThumbnailStore::GetAllThumbnailsFromDisk(MessageLoop* cb_loop) {
       NewRunnableMethod(this, &ThumbnailStore::OnDiskDataAvailable, cache));
 }
 
-void ThumbnailStore::OnDiskDataAvailable(ThumbnailStore::Cache* cache) {
+void ThumbnailStore::OnDiskDataAvailable(Cache* cache) {
   if (cache)
     cache_.reset(cache);
+
+  disk_data_loaded_ = true;
+  if (IsReady())
+    NotifyThumbnailStoreReady();
 }
 
 bool ThumbnailStore::ShouldStoreThumbnailForURL(const GURL& url) const {
-  if (IsURLBlacklisted(url) || cache_->size() >= ThumbnailStore::kMaxCacheSize)
+  if (!cache_.get())
+    return false;
+
+  if (IsURLBlacklisted(url) || cache_->size() >= kMaxCacheSize)
     return false;
 
-  return most_visited_urls_->size() < ThumbnailStore::kMaxCacheSize ||
-         IsPopular(url);
+  return IsPopular(url);
 }
 
 bool ThumbnailStore::IsURLBlacklisted(const GURL& url) const {
@@ -397,7 +441,6 @@ std::wstring ThumbnailStore::GetDictionaryKeyForURL(
 }
 
 bool ThumbnailStore::IsPopular(const GURL& url) const {
-  return most_visited_urls_->end() != find(most_visited_urls_->begin(),
-                                           most_visited_urls_->end(),
-                                           url);
+  return most_visited_urls_->size() < kMaxCacheSize ||
+         most_visited_urls_->find(url) != most_visited_urls_->end();
 }
diff --git a/chrome/browser/thumbnail_store.h b/chrome/browser/thumbnail_store.h
index 8b5fde8..143cbce 100644
--- a/chrome/browser/thumbnail_store.h
+++ b/chrome/browser/thumbnail_store.h
@@ -41,9 +41,12 @@ class ThumbnailStore : public base::RefCountedThreadSafe<ThumbnailStore>,
   ThumbnailStore();
   ~ThumbnailStore();
 
-  // Must be called after creation but before other methods are called.
-  void Init(const FilePath& db_name,      // The location of the database.
-            Profile* profile);            // To get to the HistoryService.
+  // Must be called before {Set,Get}PageThumbnail.  |db_name| is the location
+  // of an existing ThumbnailStore database or where to create a new one.
+  void Init(const FilePath& db_name, Profile* profile);
+
+  // Is the ThumbnailStore ready for GetPageThumbnail requests?
+  bool IsReady() { return disk_data_loaded_ && redirect_urls_.get(); }
 
   // Stores the given thumbnail and score with the associated url in the cache.
   bool SetPageThumbnail(const GURL& url,
@@ -83,11 +86,19 @@ class ThumbnailStore : public base::RefCountedThreadSafe<ThumbnailStore>,
   // Data structure used to store thumbnail data in memory.
   typedef std::map<GURL, CacheEntry> Cache;
 
+  // Data structre used to store the top visited URLs. It maps the end of a
+  // redirect chain to the beginning. If A -> B -> C is a redirect chain and C
+  // is a top visited url, then this map will contain an entry C => A.
+  typedef std::map<GURL, GURL> MostVisitedMap;
+
   // NotificationObserver implementation
   virtual void Observe(NotificationType type,
                        const NotificationSource& source,
                        const NotificationDetails& details);
 
+  // Notify anyone listening that the ThumbnailStore is ready to be used.
+  void NotifyThumbnailStoreReady();
+
   // Most visited URLs and their redirect lists -------------------------------
 
   // Query the HistoryService for the most visited URLs and the most recent
@@ -96,7 +107,9 @@ class ThumbnailStore : public base::RefCountedThreadSafe<ThumbnailStore>,
   void UpdateURLData();
 
   // The callback for UpdateURLData.
-  void OnURLDataAvailable(std::vector<GURL>* urls,
+  void OnURLDataAvailable(HistoryService::Handle handle,
+                          bool success,
+                          std::vector<GURL>* urls,
                           history::RedirectMap* redirects);
 
   // The callback for the redirects request to the HistoryService made in
@@ -108,6 +121,11 @@ class ThumbnailStore : public base::RefCountedThreadSafe<ThumbnailStore>,
                                   bool success,
                                   history::RedirectList* redirects);
 
+  // Search the RedirectMap for a redirect chain ending at |url|.  Returns an
+  // iterator to an entry in redirect_urls_ if found or redirect_urls_->end().
+  history::RedirectMap::iterator GetRedirectIteratorForURL(
+      const GURL& url) const;
+
   // Remove stale data --------------------------------------------------------
 
   // Remove entries from the in memory thumbnail cache cache that have been
@@ -165,9 +183,9 @@ class ThumbnailStore : public base::RefCountedThreadSafe<ThumbnailStore>,
   // and redirect information.
   scoped_refptr<HistoryService> hs_;
 
-  // A list of the most_visited_urls_ refreshed every 30mins from the
+  // The most visited urls refreshed every kUpdateIntervalSecs from the
   // HistoryService.
-  scoped_ptr<std::vector<GURL> > most_visited_urls_;
+  scoped_ptr<MostVisitedMap> most_visited_urls_;
 
   // A pointer to the persistent URL blacklist for this profile.
   const DictionaryValue* url_blacklist_;
@@ -178,8 +196,7 @@ class ThumbnailStore : public base::RefCountedThreadSafe<ThumbnailStore>,
   scoped_ptr<history::RedirectMap> redirect_urls_;
 
   // Timer on which UpdateURLData runs.
-  base::OneShotTimer<ThumbnailStore> timer_;
-  int seconds_to_next_update_;
+  base::RepeatingTimer<ThumbnailStore> timer_;
 
   // Consumer for queries to the HistoryService.
   CancelableRequestConsumer consumer_;
@@ -188,8 +205,10 @@ class ThumbnailStore : public base::RefCountedThreadSafe<ThumbnailStore>,
   NotificationRegistrar registrar_;
 
   static const unsigned int kMaxCacheSize = 24;
-  static const int64 kInitialUpdateIntervalSecs = 180;
-  static const int64 kMaxUpdateIntervalSecs = 3600;
+  static const int64 kUpdateIntervalSecs = 360;
+
+  // Has the data from disk been read?
+  bool disk_data_loaded_;
 
   DISALLOW_COPY_AND_ASSIGN(ThumbnailStore);
 };
diff --git a/chrome/browser/thumbnail_store_unittest.cc b/chrome/browser/thumbnail_store_unittest.cc
index 331d5df..cd8f146 100644
--- a/chrome/browser/thumbnail_store_unittest.cc
+++ b/chrome/browser/thumbnail_store_unittest.cc
@@ -96,8 +96,8 @@ void ThumbnailStoreTest::SetUp() {
   store_->cache_.reset(new ThumbnailStore::Cache);
   store_->redirect_urls_.reset(new history::RedirectMap);
 
-  store_->most_visited_urls_.reset(new std::vector<GURL>);
-  store_->most_visited_urls_->push_back(url_);
+  store_->most_visited_urls_.reset(new ThumbnailStore::MostVisitedMap);
+  (*store_->most_visited_urls_)[url_] = GURL();
 }
 
 void ThumbnailStoreTest::PrintPixelDiff(SkBitmap* image_a, SkBitmap* image_b) {
@@ -183,7 +183,7 @@ TEST_F(ThumbnailStoreTest, RetrieveFromDisk) {
   store_->InitializeFromDB(db_name_, NULL);
   // Write to the DB (dirty bit sould be set)
   store_->CommitCacheToDB(NULL, new ThumbnailStore::Cache(*store_->cache_));
-  store_->cache_->clear();        // Clear it from the cache.
+  store_->cache_->clear();  // Clear it from the cache.
 
   // Read from the DB.
   SQLITE_UNIQUE_STATEMENT(statement, *store_->statement_cache_,
@@ -215,7 +215,7 @@ TEST_F(ThumbnailStoreTest, FollowRedirects) {
   redirects.push_back(url_);  // url_ = http://www.google.com/
   (*store_->redirect_urls_)[my_url] = new RefCountedVector<GURL>(redirects);
 
-  store_->most_visited_urls_->push_back(my_url);
+  (*store_->most_visited_urls_)[url_] = my_url;
 
   EXPECT_TRUE(store_->SetPageThumbnail(GURL("google.com"), *google_, score_,
                                        false));
diff --git a/chrome/common/chrome_constants.cc b/chrome/common/chrome_constants.cc
index fbedb7c..2b32993 100644
--- a/chrome/common/chrome_constants.cc
+++ b/chrome/common/chrome_constants.cc
@@ -68,6 +68,7 @@ const FilePath::CharType kSafeBrowsingFilename[] = FPL("Safe Browsing");
 // chrome_process_util_linux would be broken.
 const FilePath::CharType kSingletonSocketFilename[] = FPL("SingletonSocket");
 const FilePath::CharType kThumbnailsFilename[] = FPL("Thumbnails");
+const FilePath::CharType kNewTabThumbnailsFilename[] = FPL("Top Thumbnails");
 const wchar_t kUserDataDirname[] = L"User Data";
 const FilePath::CharType kUserScriptsDirname[] = FPL("User Scripts");
 const FilePath::CharType kWebDataFilename[] = FPL("Web Data");
diff --git a/chrome/common/chrome_constants.h b/chrome/common/chrome_constants.h
index 4f9f4a1..350c835 100644
--- a/chrome/common/chrome_constants.h
+++ b/chrome/common/chrome_constants.h
@@ -37,6 +37,7 @@ extern const FilePath::CharType kPreferencesFilename[];
 extern const FilePath::CharType kSafeBrowsingFilename[];
 extern const FilePath::CharType kSingletonSocketFilename[];
 extern const FilePath::CharType kThumbnailsFilename[];
+extern const FilePath::CharType kNewTabThumbnailsFilename[];
 extern const wchar_t kUserDataDirname[];
 extern const FilePath::CharType kUserScriptsDirname[];
 extern const FilePath::CharType kWebDataFilename[];
diff --git a/chrome/common/notification_type.h b/chrome/common/notification_type.h
index 221bf32..04fc94f 100644
--- a/chrome/common/notification_type.h
+++ b/chrome/common/notification_type.h
@@ -471,6 +471,12 @@ class NotificationType {
     // history_notifications.h).
     FAVICON_CHANGED,
 
+    // Thumbnails---------------------------------------------------------------
+
+    // Set by ThumbnailStore when it was finished loading data from disk on
+    // startup.
+    THUMBNAIL_STORE_READY,
+
     // Bookmarks ---------------------------------------------------------------
 
     // Sent when the starred state of a URL changes. A URL is starred if there