Revert 113071 - Revert 113047 - Make ExtensionService use ExtensionSet.

ExtensionManagementApiBrowserTest.LaunchApp fixed by r113141.

Make ExtensionSet iterate like a set instead of a map.

BUG=104091
TEST=existing tests

Review URL: http://codereview.chromium.org/8733004

TBR=yoz@chromium.org
Review URL: http://codereview.chromium.org/8789018

TBR=yoz@chromium.org
Review URL: http://codereview.chromium.org/8822021

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113233 0039d316-1c4b-4281-b951-d872f2087c98

53 files changed, 499 insertions, 485 deletions

diff --git a/chrome/browser/autocomplete/extension_app_provider.cc b/chrome/browser/autocomplete/extension_app_provider.cc
index b3ceac1..8365cb1 100644
--- a/chrome/browser/autocomplete/extension_app_provider.cc
+++ b/chrome/browser/autocomplete/extension_app_provider.cc
@@ -98,9 +98,9 @@ void ExtensionAppProvider::RefreshAppList() {
   ExtensionService* extension_service = profile_->GetExtensionService();
   if (!extension_service)
     return;  // During testing, there is no extension service.
-  const ExtensionList* extensions = extension_service->extensions();
+  const ExtensionSet* extensions = extension_service->extensions();
   extension_apps_.clear();
-  for (ExtensionList::const_iterator app = extensions->begin();
+  for (ExtensionSet::const_iterator app = extensions->begin();
        app != extensions->end(); ++app) {
     if ((*app)->is_app() && (*app)->GetFullLaunchURL().is_valid()) {
       if (profile_->IsOffTheRecord() &&
diff --git a/chrome/browser/automation/automation_provider_observers.cc b/chrome/browser/automation/automation_provider_observers.cc
index a2decb9..670d01e 100644
--- a/chrome/browser/automation/automation_provider_observers.cc
+++ b/chrome/browser/automation/automation_provider_observers.cc
@@ -2018,11 +2018,11 @@ namespace {
 // as identified from a given list of extensions.  The caller takes ownership
 // of the created vector.
 std::vector<DictionaryValue*>* GetAppInfoFromExtensions(
-    const ExtensionList* extensions,
+    const ExtensionSet* extensions,
     ExtensionService* ext_service) {
   std::vector<DictionaryValue*>* apps_list =
       new std::vector<DictionaryValue*>();
-  for (ExtensionList::const_iterator ext = extensions->begin();
+  for (ExtensionSet::const_iterator ext = extensions->begin();
        ext != extensions->end(); ++ext) {
     // Only return information about extensions that are actually apps.
     if ((*ext)->is_app()) {
@@ -2090,7 +2090,7 @@ NTPInfoObserver::NTPInfoObserver(
   }
   // Process enabled extensions.
   ListValue* apps_list = new ListValue();
-  const ExtensionList* extensions = ext_service->extensions();
+  const ExtensionSet* extensions = ext_service->extensions();
   std::vector<DictionaryValue*>* enabled_apps = GetAppInfoFromExtensions(
       extensions, ext_service);
   for (std::vector<DictionaryValue*>::const_iterator app =
@@ -2100,7 +2100,7 @@ NTPInfoObserver::NTPInfoObserver(
   }
   delete enabled_apps;
   // Process disabled extensions.
-  const ExtensionList* disabled_extensions = ext_service->disabled_extensions();
+  const ExtensionSet* disabled_extensions = ext_service->disabled_extensions();
   std::vector<DictionaryValue*>* disabled_apps = GetAppInfoFromExtensions(
       disabled_extensions, ext_service);
   for (std::vector<DictionaryValue*>::const_iterator app =
@@ -2110,7 +2110,7 @@ NTPInfoObserver::NTPInfoObserver(
   }
   delete disabled_apps;
   // Process terminated extensions.
-  const ExtensionList* terminated_extensions =
+  const ExtensionSet* terminated_extensions =
       ext_service->terminated_extensions();
   std::vector<DictionaryValue*>* terminated_apps = GetAppInfoFromExtensions(
       terminated_extensions, ext_service);
diff --git a/chrome/browser/automation/testing_automation_provider.cc b/chrome/browser/automation/testing_automation_provider.cc
index 3230157..498c512 100644
--- a/chrome/browser/automation/testing_automation_provider.cc
+++ b/chrome/browser/automation/testing_automation_provider.cc
@@ -4381,8 +4381,8 @@ void TestingAutomationProvider::GetExtensionsInfo(
   }
   scoped_ptr<DictionaryValue> return_value(new DictionaryValue);
   ListValue* extensions_values = new ListValue;
-  const ExtensionList* extensions = service->extensions();
-  const ExtensionList* disabled_extensions = service->disabled_extensions();
+  const ExtensionSet* extensions = service->extensions();
+  const ExtensionSet* disabled_extensions = service->disabled_extensions();
   ExtensionList all;
   all.insert(all.end(),
              extensions->begin(),
diff --git a/chrome/browser/background/background_application_list_model.cc b/chrome/browser/background/background_application_list_model.cc
index 6550ba2..d7d4740 100644
--- a/chrome/browser/background/background_application_list_model.cc
+++ b/chrome/browser/background/background_application_list_model.cc
@@ -71,9 +71,9 @@ class BackgroundApplicationListModel::Application
 namespace {
 void GetServiceApplications(ExtensionService* service,
                             ExtensionList* applications_result) {
-  const ExtensionList* extensions = service->extensions();
+  const ExtensionSet* extensions = service->extensions();
 
-  for (ExtensionList::const_iterator cursor = extensions->begin();
+  for (ExtensionSet::const_iterator cursor = extensions->begin();
        cursor != extensions->end();
        ++cursor) {
     const Extension* extension = *cursor;
@@ -84,7 +84,7 @@ void GetServiceApplications(ExtensionService* service,
   // Walk the list of terminated extensions also (just because an extension
   // crashed doesn't mean we should ignore it).
   extensions = service->terminated_extensions();
-  for (ExtensionList::const_iterator cursor = extensions->begin();
+  for (ExtensionSet::const_iterator cursor = extensions->begin();
        cursor != extensions->end();
        ++cursor) {
     const Extension* extension = *cursor;
diff --git a/chrome/browser/background/background_application_list_model_unittest.cc b/chrome/browser/background/background_application_list_model_unittest.cc
index f3fff07..4024fad 100644
--- a/chrome/browser/background/background_application_list_model_unittest.cc
+++ b/chrome/browser/background/background_application_list_model_unittest.cc
@@ -60,8 +60,11 @@ static scoped_refptr<Extension> CreateExtension(const std::string& name,
   }
   std::string error;
   scoped_refptr<Extension> extension = Extension::Create(
-      bogus_file_path().AppendASCII(name), Extension::INVALID, manifest,
-      Extension::STRICT_ERROR_CHECKS, &error);
+      bogus_file_path().AppendASCII(name),
+      Extension::INVALID,
+      manifest,
+      Extension::STRICT_ERROR_CHECKS,
+      &error);
   // Cannot ASSERT_* here because that attempts an illegitimate return.
   // Cannot EXPECT_NE here because that assumes non-pointers unlike EXPECT_EQ
   EXPECT_TRUE(extension.get() != NULL) << error;
@@ -105,7 +108,7 @@ TEST_F(BackgroundApplicationListModelTest, ExplicitTest) {
   ASSERT_TRUE(service);
   ASSERT_TRUE(service->is_ready());
   ASSERT_TRUE(service->extensions());
-  ASSERT_TRUE(service->extensions()->empty());
+  ASSERT_TRUE(service->extensions()->is_empty());
   scoped_ptr<BackgroundApplicationListModel> model(
       new BackgroundApplicationListModel(profile_.get()));
   ASSERT_EQ(0U, model->size());
@@ -171,7 +174,7 @@ TEST_F(BackgroundApplicationListModelTest, AddRemovePermissionsTest) {
   ASSERT_TRUE(service);
   ASSERT_TRUE(service->is_ready());
   ASSERT_TRUE(service->extensions());
-  ASSERT_TRUE(service->extensions()->empty());
+  ASSERT_TRUE(service->extensions()->is_empty());
   scoped_ptr<BackgroundApplicationListModel> model(
       new BackgroundApplicationListModel(profile_.get()));
   ASSERT_EQ(0U, model->size());
@@ -310,7 +313,7 @@ TEST_F(BackgroundApplicationListModelTest, RandomTest) {
   ASSERT_TRUE(service);
   ASSERT_TRUE(service->is_ready());
   ASSERT_TRUE(service->extensions());
-  ASSERT_TRUE(service->extensions()->empty());
+  ASSERT_TRUE(service->extensions()->is_empty());
   scoped_ptr<BackgroundApplicationListModel> model(
       new BackgroundApplicationListModel(profile_.get()));
   ASSERT_EQ(0U, model->size());
diff --git a/chrome/browser/background/background_contents_service.cc b/chrome/browser/background/background_contents_service.cc
index 1bc42a5..16f7bf7 100644
--- a/chrome/browser/background/background_contents_service.cc
+++ b/chrome/browser/background/background_contents_service.cc
@@ -418,9 +418,9 @@ void BackgroundContentsService::LoadBackgroundContentsFromDictionary(
 
 void BackgroundContentsService::LoadBackgroundContentsFromManifests(
     Profile* profile) {
-  const ExtensionList* extensions =
+  const ExtensionSet* extensions =
       profile->GetExtensionService()->extensions();
-  ExtensionList::const_iterator iter = extensions->begin();
+  ExtensionSet::const_iterator iter = extensions->begin();
   for (; iter != extensions->end(); ++iter) {
     const Extension* extension = *iter;
     if (extension->is_hosted_app() &&
diff --git a/chrome/browser/debugger/devtools_window.cc b/chrome/browser/debugger/devtools_window.cc
index 9d1dd6b..2a1fb5e 100644
--- a/chrome/browser/debugger/devtools_window.cc
+++ b/chrome/browser/debugger/devtools_window.cc
@@ -414,9 +414,9 @@ void DevToolsWindow::AddDevToolsExtensionsToClient() {
   if (!extension_service)
     return;
 
-  const ExtensionList* extensions = extension_service->extensions();
+  const ExtensionSet* extensions = extension_service->extensions();
 
-  for (ExtensionList::const_iterator extension = extensions->begin();
+  for (ExtensionSet::const_iterator extension = extensions->begin();
        extension != extensions->end(); ++extension) {
     if ((*extension)->devtools_url().is_empty())
       continue;
diff --git a/chrome/browser/extensions/browser_action_apitest.cc b/chrome/browser/extensions/browser_action_apitest.cc
index 943eaa7..08e65fd 100644
--- a/chrome/browser/extensions/browser_action_apitest.cc
+++ b/chrome/browser/extensions/browser_action_apitest.cc
@@ -316,12 +316,15 @@ IN_PROC_BROWSER_TEST_F(BrowserActionApiTest, IncognitoDragging) {
 
   const size_t size_before = service->extensions()->size();
 
-  ASSERT_TRUE(LoadExtension(test_data_dir_.AppendASCII(
-      "browser_action/basics")));
-  ASSERT_TRUE(LoadExtension(test_data_dir_.AppendASCII(
-      "browser_action/popup")));
-  ASSERT_TRUE(LoadExtension(test_data_dir_.AppendASCII(
-      "browser_action/add_popup")));
+  const Extension* extension_a = LoadExtension(test_data_dir_.AppendASCII(
+      "browser_action/basics"));
+  const Extension* extension_b = LoadExtension(test_data_dir_.AppendASCII(
+      "browser_action/popup"));
+  const Extension* extension_c = LoadExtension(test_data_dir_.AppendASCII(
+      "browser_action/add_popup"));
+  ASSERT_TRUE(extension_a);
+  ASSERT_TRUE(extension_b);
+  ASSERT_TRUE(extension_c);
 
   // Test that there are 3 browser actions in the toolbar.
   ASSERT_EQ(size_before + 3, service->extensions()->size());
@@ -329,10 +332,8 @@ IN_PROC_BROWSER_TEST_F(BrowserActionApiTest, IncognitoDragging) {
 
   // Now enable 2 of the extensions in incognito mode, and test that the browser
   // actions show up.
-  service->extension_prefs()->SetIsIncognitoEnabled(
-      service->extensions()->at(size_before)->id(), true);
-  service->extension_prefs()->SetIsIncognitoEnabled(
-      service->extensions()->at(size_before + 2)->id(), true);
+  service->extension_prefs()->SetIsIncognitoEnabled(extension_a->id(), true);
+  service->extension_prefs()->SetIsIncognitoEnabled(extension_c->id(), true);
 
   Profile* incognito_profile = browser()->profile()->GetOffTheRecordProfile();
   Browser* incognito_browser = Browser::Create(incognito_profile);
@@ -355,8 +356,7 @@ IN_PROC_BROWSER_TEST_F(BrowserActionApiTest, IncognitoDragging) {
   // regular and incognito mode.
 
   // ABC -> CAB
-  service->toolbar_model()->MoveBrowserAction(
-      service->extensions()->at(size_before + 2), 0);
+  service->toolbar_model()->MoveBrowserAction(extension_c, 0);
 
   EXPECT_EQ(kTooltipC, GetBrowserActionsBar().GetTooltip(0));
   EXPECT_EQ(kTooltipA, GetBrowserActionsBar().GetTooltip(1));
@@ -366,8 +366,7 @@ IN_PROC_BROWSER_TEST_F(BrowserActionApiTest, IncognitoDragging) {
   EXPECT_EQ(kTooltipA, incognito_bar.GetTooltip(1));
 
   // CAB -> CBA
-  service->toolbar_model()->MoveBrowserAction(
-      service->extensions()->at(size_before + 1), 1);
+  service->toolbar_model()->MoveBrowserAction(extension_b, 1);
 
   EXPECT_EQ(kTooltipC, GetBrowserActionsBar().GetTooltip(0));
   EXPECT_EQ(kTooltipB, GetBrowserActionsBar().GetTooltip(1));
diff --git a/chrome/browser/extensions/component_loader_unittest.cc b/chrome/browser/extensions/component_loader_unittest.cc
index 3e3d8c8..89f4762 100644
--- a/chrome/browser/extensions/component_loader_unittest.cc
+++ b/chrome/browser/extensions/component_loader_unittest.cc
@@ -11,6 +11,7 @@
 #include "chrome/browser/extensions/test_extension_service.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/extensions/extension.h"
+#include "chrome/common/extensions/extension_set.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/test/base/testing_pref_service.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -20,7 +21,7 @@ namespace {
 class MockExtensionService : public TestExtensionService {
  private:
   bool ready_;
-  ExtensionList extension_list_;
+  ExtensionSet extension_set_;
 
  public:
   MockExtensionService() : ready_(false) {
@@ -28,37 +29,30 @@ class MockExtensionService : public TestExtensionService {
 
   virtual void AddExtension(const Extension* extension) OVERRIDE {
     // ExtensionService must become the owner of the extension object.
-    extension_list_.push_back(extension);
+    extension_set_.Insert(extension);
   }
 
   virtual void UnloadExtension(
       const std::string& extension_id,
       extension_misc::UnloadedExtensionReason reason) OVERRIDE {
     // Remove the extension with the matching id.
-    for (ExtensionList::iterator it = extension_list_.begin();
-         it != extension_list_.end();
-         ++it) {
-      if ((*it)->id() == extension_id) {
-        extension_list_.erase(it);
-        return;
-      }
-    }
+    extension_set_.Remove(extension_id);
   }
 
   virtual bool is_ready() OVERRIDE {
     return ready_;
   }
 
-  virtual const ExtensionList* extensions() const OVERRIDE {
-    return &extension_list_;
+  virtual const ExtensionSet* extensions() const OVERRIDE {
+    return &extension_set_;
   }
 
   void set_ready(bool ready) {
     ready_ = ready;
   }
 
-  void clear_extension_list() {
-    extension_list_.clear();
+  void clear_extensions() {
+    extension_set_.Clear();
   }
 };
 
@@ -217,7 +211,7 @@ TEST_F(ComponentLoaderTest, LoadAll) {
   unsigned int default_count = extension_service_.extensions()->size();
 
   // Clear the list of loaded extensions, and reload with one more.
-  extension_service_.clear_extension_list();
+  extension_service_.clear_extensions();
   component_loader_.Add(manifest_contents_, extension_path_);
   component_loader_.LoadAll();
 
@@ -237,7 +231,7 @@ TEST_F(ComponentLoaderTest, EnterpriseWebStore) {
 
   // Now that the pref is set, check if it's added by default.
   extension_service_.set_ready(false);
-  extension_service_.clear_extension_list();
+  extension_service_.clear_extensions();
   component_loader_.ClearAllRegistered();
   component_loader_.AddDefaultComponentExtensions();
   component_loader_.LoadAll();
diff --git a/chrome/browser/extensions/extension_apitest.cc b/chrome/browser/extensions/extension_apitest.cc
index 893a25d..624f036 100644
--- a/chrome/browser/extensions/extension_apitest.cc
+++ b/chrome/browser/extensions/extension_apitest.cc
@@ -202,28 +202,29 @@ bool ExtensionApiTest::RunExtensionTestImpl(const char* extension_name,
   }
 }
 
-// Test that exactly one extension loaded.
+// Test that exactly one extension is loaded, and return it.
 const Extension* ExtensionApiTest::GetSingleLoadedExtension() {
   ExtensionService* service = browser()->profile()->GetExtensionService();
 
-  int found_extension_index = -1;
-  for (size_t i = 0; i < service->extensions()->size(); ++i) {
+  const Extension* extension = NULL;
+  for (ExtensionSet::const_iterator it = service->extensions()->begin();
+       it != service->extensions()->end(); ++it) {
     // Ignore any component extensions. They are automatically loaded into all
     // profiles and aren't the extension we're looking for here.
-    if (service->extensions()->at(i)->location() == Extension::COMPONENT)
+    if ((*it)->location() == Extension::COMPONENT)
       continue;
 
-    if (found_extension_index != -1) {
+    if (extension != NULL) {
+      // TODO(yoz): this is misleading; it counts component extensions.
       message_ = base::StringPrintf(
           "Expected only one extension to be present.  Found %u.",
           static_cast<unsigned>(service->extensions()->size()));
       return NULL;
     }
 
-    found_extension_index = static_cast<int>(i);
+    extension = *it;
   }
 
-  const Extension* extension = service->extensions()->at(found_extension_index);
   if (!extension) {
     message_ = "extension pointer is NULL.";
     return NULL;
diff --git a/chrome/browser/extensions/extension_browsertest.cc b/chrome/browser/extensions/extension_browsertest.cc
index b3f3d1b..339a28c 100644
--- a/chrome/browser/extensions/extension_browsertest.cc
+++ b/chrome/browser/extensions/extension_browsertest.cc
@@ -72,13 +72,13 @@ const Extension* ExtensionBrowserTest::LoadExtensionWithOptions(
     ui_test_utils::RunMessageLoop();
   }
 
-  // Find the extension by iterating backwards since it is likely last.
+  // Find the loaded extension by its path. See crbug.com/59531 for why
+  // we cannot just use last_loaded_extension_id_.
   FilePath extension_path = path;
   file_util::AbsolutePath(&extension_path);
   const Extension* extension = NULL;
-  for (ExtensionList::const_reverse_iterator iter =
-           service->extensions()->rbegin();
-       iter != service->extensions()->rend(); ++iter) {
+  for (ExtensionSet::const_iterator iter = service->extensions()->begin();
+       iter != service->extensions()->end(); ++iter) {
     if ((*iter)->path() == extension_path) {
       extension = *iter;
       break;
@@ -296,8 +296,9 @@ const Extension* ExtensionBrowserTest::InstallOrUpdateExtension(
             << " num after: " << base::IntToString(num_after)
             << " Installed extensions follow:";
 
-    for (size_t i = 0; i < service->extensions()->size(); ++i)
-      VLOG(1) << "  " << (*service->extensions())[i]->id();
+    for (ExtensionSet::const_iterator it = service->extensions()->begin();
+         it != service->extensions()->end(); ++it)
+      VLOG(1) << "  " << (*it)->id();
 
     VLOG(1) << "Errors follow:";
     const std::vector<std::string>* errors =
diff --git a/chrome/browser/extensions/extension_browsertests_misc.cc b/chrome/browser/extensions/extension_browsertests_misc.cc
index 5d843aa..86e3da7 100644
--- a/chrome/browser/extensions/extension_browsertests_misc.cc
+++ b/chrome/browser/extensions/extension_browsertests_misc.cc
@@ -212,29 +212,30 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, PageActionRefreshCrash) {
   FilePath base_path = test_data_dir_.AppendASCII("browsertest")
                                      .AppendASCII("crash_44415");
   // Load extension A.
-  ASSERT_TRUE(LoadExtension(base_path.AppendASCII("ExtA")));
+  const Extension* extensionA = LoadExtension(base_path.AppendASCII("ExtA"));
+  ASSERT_TRUE(extensionA);
   ASSERT_TRUE(WaitForPageActionVisibilityChangeTo(1));
   ASSERT_EQ(size_before + 1, service->extensions()->size());
-  const Extension* extensionA = service->extensions()->at(size_before);
 
   LOG(INFO) << "Load extension A done  : "
             << (base::TimeTicks::Now() - start_time).InMilliseconds()
             << " ms" << std::flush;
 
   // Load extension B.
-  ASSERT_TRUE(LoadExtension(base_path.AppendASCII("ExtB")));
+  const Extension* extensionB = LoadExtension(base_path.AppendASCII("ExtB"));
+  ASSERT_TRUE(extensionB);
   ASSERT_TRUE(WaitForPageActionVisibilityChangeTo(2));
   ASSERT_EQ(size_before + 2, service->extensions()->size());
-  const Extension* extensionB = service->extensions()->at(size_before + 1);
 
   LOG(INFO) << "Load extension B done  : "
             << (base::TimeTicks::Now() - start_time).InMilliseconds()
             << " ms" << std::flush;
 
+  std::string idA = extensionA->id();
   ReloadExtension(extensionA->id());
   // ExtensionA has changed, so refetch it.
   ASSERT_EQ(size_before + 2, service->extensions()->size());
-  extensionA = service->extensions()->at(size_before + 1);
+  extensionA = service->extensions()->GetByID(idA);
 
   LOG(INFO) << "Reload extension A done: "
             << (base::TimeTicks::Now() - start_time).InMilliseconds()
@@ -278,10 +279,10 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, TitleLocalizationBrowserAction) {
   const size_t size_before = service->extensions()->size();
   FilePath extension_path(test_data_dir_.AppendASCII("browsertest")
                                         .AppendASCII("title_localized"));
-  ASSERT_TRUE(LoadExtension(extension_path));
+  const Extension* extension = LoadExtension(extension_path);
+  ASSERT_TRUE(extension);
 
   ASSERT_EQ(size_before + 1, service->extensions()->size());
-  const Extension* extension = service->extensions()->at(size_before);
 
   EXPECT_STREQ(WideToUTF8(L"Hreggvi\u00F0ur: l10n browser action").c_str(),
                extension->description().c_str());
@@ -302,7 +303,8 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, TitleLocalizationPageAction) {
 
   FilePath extension_path(test_data_dir_.AppendASCII("browsertest")
                                         .AppendASCII("title_localized_pa"));
-  ASSERT_TRUE(LoadExtension(extension_path));
+  const Extension* extension = LoadExtension(extension_path);
+  ASSERT_TRUE(extension);
 
   // Any navigation prompts the location bar to load the page action.
   GURL url = test_server()->GetURL(kLocalization);
@@ -310,7 +312,6 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, TitleLocalizationPageAction) {
   ASSERT_TRUE(WaitForPageActionVisibilityChangeTo(1));
 
   ASSERT_EQ(size_before + 1, service->extensions()->size());
-  const Extension* extension = service->extensions()->at(size_before);
 
   EXPECT_STREQ(WideToUTF8(L"Hreggvi\u00F0ur: l10n page action").c_str(),
                extension->description().c_str());
@@ -387,6 +388,7 @@ bool ValidatePageElement(TabContents* tab,
 void NavigateToFeedAndValidate(net::TestServer* server,
                                const std::string& url,
                                Browser* browser,
+                               std::string extension_id,
                                bool sniff_xml_type,
                                const std::string& expected_feed_title,
                                const std::string& expected_item_title,
@@ -396,12 +398,9 @@ void NavigateToFeedAndValidate(net::TestServer* server,
     // TODO(finnur): Implement this is a non-flaky way.
   }
 
-  ExtensionService* service = browser->profile()->GetExtensionService();
-  const Extension* extension = service->extensions()->back();
-  std::string id = extension->id();
-
   // Navigate to the subscribe page directly.
-  ui_test_utils::NavigateToURL(browser, GetFeedUrl(server, url, true, id));
+  ui_test_utils::NavigateToURL(browser,
+                               GetFeedUrl(server, url, true, extension_id));
 
   TabContents* tab = browser->GetSelectedTabContents();
   ASSERT_TRUE(ValidatePageElement(tab,
@@ -425,10 +424,12 @@ void NavigateToFeedAndValidate(net::TestServer* server,
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed1) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
-  NavigateToFeedAndValidate(test_server(), kValidFeed1, browser(), true,
+  NavigateToFeedAndValidate(test_server(), kValidFeed1, browser(), id, true,
                             "Feed for MyFeedTitle",
                             "Title 1",
                             "Desc",
@@ -438,10 +439,12 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed1) {
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed2) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
-  NavigateToFeedAndValidate(test_server(), kValidFeed2, browser(), true,
+  NavigateToFeedAndValidate(test_server(), kValidFeed2, browser(), id, true,
                             "Feed for MyFeed2",
                             "My item title1",
                             "This is a summary.",
@@ -451,10 +454,12 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed2) {
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed3) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
-  NavigateToFeedAndValidate(test_server(), kValidFeed3, browser(), true,
+  NavigateToFeedAndValidate(test_server(), kValidFeed3, browser(), id, true,
                             "Feed for Google Code buglist rss feed",
                             "My dear title",
                             "My dear content",
@@ -464,10 +469,12 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed3) {
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed4) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
-  NavigateToFeedAndValidate(test_server(), kValidFeed4, browser(), true,
+  NavigateToFeedAndValidate(test_server(), kValidFeed4, browser(), id, true,
                             "Feed for Title chars <script> %23 stop",
                             "Title chars  %23 stop",
                             "My dear content %23 stop",
@@ -477,12 +484,14 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed4) {
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed0) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
   // Try a feed with a link with an onclick handler (before r27440 this would
   // trigger a NOTREACHED).
-  NavigateToFeedAndValidate(test_server(), kValidFeed0, browser(), true,
+  NavigateToFeedAndValidate(test_server(), kValidFeed0, browser(), id, true,
                             "Feed for MyFeedTitle",
                             "Title 1",
                             "Desc VIDEO",
@@ -492,11 +501,13 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed0) {
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed5) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
   // Feed with valid but mostly empty xml.
-  NavigateToFeedAndValidate(test_server(), kValidFeed5, browser(), true,
+  NavigateToFeedAndValidate(test_server(), kValidFeed5, browser(), id, true,
                             "Feed for Unknown feed name",
                             "element 'anchor_0' not found",
                             "element 'desc_0' not found",
@@ -506,11 +517,13 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed5) {
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed6) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
   // Feed that is technically invalid but still parseable.
-  NavigateToFeedAndValidate(test_server(), kValidFeed6, browser(), true,
+  NavigateToFeedAndValidate(test_server(), kValidFeed6, browser(), id, true,
                             "Feed for MyFeedTitle",
                             "Title 1",
                             "Desc",
@@ -520,11 +533,13 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeed6) {
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedInvalidFeed1) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
   // Try an empty feed.
-  NavigateToFeedAndValidate(test_server(), kInvalidFeed1, browser(), false,
+  NavigateToFeedAndValidate(test_server(), kInvalidFeed1, browser(), id, false,
                             "Feed for Unknown feed name",
                             "element 'anchor_0' not found",
                             "element 'desc_0' not found",
@@ -534,11 +549,13 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedInvalidFeed1) {
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedInvalidFeed2) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
   // Try a garbage feed.
-  NavigateToFeedAndValidate(test_server(), kInvalidFeed2, browser(), false,
+  NavigateToFeedAndValidate(test_server(), kInvalidFeed2, browser(), id, false,
                             "Feed for Unknown feed name",
                             "element 'anchor_0' not found",
                             "element 'desc_0' not found",
@@ -548,11 +565,13 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedInvalidFeed2) {
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedInvalidFeed3) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
   // Try a feed that doesn't exist.
-  NavigateToFeedAndValidate(test_server(), "foo.xml", browser(), false,
+  NavigateToFeedAndValidate(test_server(), "foo.xml", browser(), id, false,
                             "Feed for Unknown feed name",
                             "element 'anchor_0' not found",
                             "element 'desc_0' not found",
@@ -562,8 +581,10 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedInvalidFeed3) {
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedInvalidFeed4) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
   // subscribe.js shouldn't double-decode the URL passed in. Otherwise feed
   // links such as http://search.twitter.com/search.atom?lang=en&q=%23chrome
@@ -572,25 +593,29 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedInvalidFeed4) {
   // uses an underscore instead of a hash, but the principle is the same. If
   // we start erroneously double decoding again, the path (and the feed) will
   // become valid resulting in a failure for this test.
-  NavigateToFeedAndValidate(test_server(), kFeedTripleEncoded, browser(), true,
-                            "Feed for Unknown feed name",
-                            "element 'anchor_0' not found",
-                            "element 'desc_0' not found",
-                            "This feed contains no entries.");
+  NavigateToFeedAndValidate(
+      test_server(), kFeedTripleEncoded, browser(), id, true,
+      "Feed for Unknown feed name",
+      "element 'anchor_0' not found",
+      "element 'desc_0' not found",
+      "This feed contains no entries.");
 }
 
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, ParseFeedValidFeedNoLinks) {
   ASSERT_TRUE(test_server()->Start());
 
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("subscribe_page_action")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("subscribe_page_action"));
+  ASSERT_TRUE(extension);
+  std::string id = extension->id();
 
   // Valid feed but containing no links.
-  NavigateToFeedAndValidate(test_server(), kValidFeedNoLinks, browser(), true,
-                            "Feed for MyFeedTitle",
-                            "Title with no link",
-                            "Desc",
-                            "No error");
+  NavigateToFeedAndValidate(
+      test_server(), kValidFeedNoLinks, browser(), id, true,
+      "Feed for MyFeedTitle",
+      "Title with no link",
+      "Desc",
+      "No error");
 }
 
 // Tests that an error raised during an async function still fires
@@ -722,7 +747,8 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, MAYBE_PluginLoadUnload) {
   ExtensionService* service = browser()->profile()->GetExtensionService();
   service->set_show_extensions_prompts(false);
   const size_t size_before = service->extensions()->size();
-  ASSERT_TRUE(LoadExtension(extension_dir));
+  const Extension* extension = LoadExtension(extension_dir);
+  ASSERT_TRUE(extension);
   EXPECT_EQ(size_before + 1, service->extensions()->size());
   // Now the plugin should be in the cache, but we have to reload the page for
   // it to work.
@@ -742,7 +768,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, MAYBE_PluginLoadUnload) {
   EXPECT_TRUE(result);
 
   EXPECT_EQ(size_before + 1, service->extensions()->size());
-  UnloadExtension(service->extensions()->at(size_before)->id());
+  UnloadExtension(extension->id());
   EXPECT_EQ(size_before, service->extensions()->size());
 
   // Now the plugin should be unloaded, and the page should be broken.
@@ -784,11 +810,11 @@ IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, MAYBE_PluginPrivate) {
   ExtensionService* service = browser()->profile()->GetExtensionService();
   service->set_show_extensions_prompts(false);
   const size_t size_before = service->extensions()->size();
-  ASSERT_TRUE(LoadExtension(extension_dir));
+  const Extension* extension = LoadExtension(extension_dir);
+  ASSERT_TRUE(extension);
   EXPECT_EQ(size_before + 1, service->extensions()->size());
 
   // Load the test page through the extension URL, and the plugin should work.
-  const Extension* extension = service->extensions()->back();
   ui_test_utils::NavigateToURL(browser(),
       extension->GetResourceURL("test.html"));
   TabContents* tab = browser()->GetSelectedTabContents();
@@ -825,11 +851,11 @@ static const wchar_t* jscript_click_option_button =
 // Disabled.  See http://crbug.com/26948 for details.
 IN_PROC_BROWSER_TEST_F(ExtensionBrowserTest, DISABLED_OptionsPage) {
   // Install an extension with an options page.
-  ASSERT_TRUE(InstallExtension(test_data_dir_.AppendASCII("options.crx"), 1));
+  const Extension* extension =
+      InstallExtension(test_data_dir_.AppendASCII("options.crx"), 1);
+  ASSERT_TRUE(extension);
   ExtensionService* service = browser()->profile()->GetExtensionService();
-  const ExtensionList* extensions = service->extensions();
-  ASSERT_EQ(1u, extensions->size());
-  const Extension* extension = extensions->at(0);
+  ASSERT_EQ(1u, service->extensions()->size());
 
   // Go to the Extension Settings page and click the Options button.
   ui_test_utils::NavigateToURL(
diff --git a/chrome/browser/extensions/extension_context_menu_browsertest.cc b/chrome/browser/extensions/extension_context_menu_browsertest.cc
index 1fe2247..2be1464 100644
--- a/chrome/browser/extensions/extension_context_menu_browsertest.cc
+++ b/chrome/browser/extensions/extension_context_menu_browsertest.cc
@@ -156,9 +156,9 @@ class ExtensionContextMenuBrowserTest : public ExtensionBrowserTest {
   // Returns a pointer to the currently loaded extension with |name|, or null
   // if not found.
   const Extension* GetExtensionNamed(std::string name) {
-    const ExtensionList* extensions =
+    const ExtensionSet* extensions =
         browser()->profile()->GetExtensionService()->extensions();
-    ExtensionList::const_iterator i;
+    ExtensionSet::const_iterator i;
     for (i = extensions->begin(); i != extensions->end(); ++i) {
       if ((*i)->name() == name) {
         return *i;
diff --git a/chrome/browser/extensions/extension_crash_recovery_browsertest.cc b/chrome/browser/extensions/extension_crash_recovery_browsertest.cc
index 6ee66af..2dd874a 100644
--- a/chrome/browser/extensions/extension_crash_recovery_browsertest.cc
+++ b/chrome/browser/extensions/extension_crash_recovery_browsertest.cc
@@ -62,12 +62,10 @@ class ExtensionCrashRecoveryTest : public ExtensionBrowserTest {
     return balloons.size();
   }
 
-  void CrashExtension(size_t index) {
-    ASSERT_LT(index, GetExtensionService()->extensions()->size());
+  void CrashExtension(std::string extension_id) {
     const Extension* extension =
-        GetExtensionService()->extensions()->at(index);
+        GetExtensionService()->extensions()->GetByID(extension_id);
     ASSERT_TRUE(extension);
-    std::string extension_id(extension->id());
     ExtensionHost* extension_host = GetExtensionProcessManager()->
         GetBackgroundHostForExtension(extension_id);
     ASSERT_TRUE(extension_host);
@@ -81,43 +79,36 @@ class ExtensionCrashRecoveryTest : public ExtensionBrowserTest {
                  GetBackgroundHostForExtension(extension_id));
   }
 
-  void CheckExtensionConsistency(size_t index) {
-    ASSERT_LT(index, GetExtensionService()->extensions()->size());
+  void CheckExtensionConsistency(std::string extension_id) {
     const Extension* extension =
-        GetExtensionService()->extensions()->at(index);
+        GetExtensionService()->extensions()->GetByID(extension_id);
     ASSERT_TRUE(extension);
     ExtensionHost* extension_host = GetExtensionProcessManager()->
-        GetBackgroundHostForExtension(extension->id());
+        GetBackgroundHostForExtension(extension_id);
     ASSERT_TRUE(extension_host);
     ASSERT_TRUE(GetExtensionProcessManager()->HasExtensionHost(extension_host));
     ASSERT_TRUE(extension_host->IsRenderViewLive());
     extensions::ProcessMap* process_map =
         browser()->profile()->GetExtensionService()->process_map();
     ASSERT_TRUE(process_map->Contains(
-        extension->id(), extension_host->render_view_host()->process()->
-            GetID()));
+        extension_id, extension_host->render_view_host()->process()->GetID()));
   }
 
   void LoadTestExtension() {
     ExtensionBrowserTest::SetUpInProcessBrowserTestFixture();
-    const size_t size_before = GetExtensionService()->extensions()->size();
-    ASSERT_TRUE(LoadExtension(
-        test_data_dir_.AppendASCII("common").AppendASCII("background_page")));
-    const Extension* extension = GetExtensionService()->extensions()->back();
+    const Extension* extension = LoadExtension(
+        test_data_dir_.AppendASCII("common").AppendASCII("background_page"));
     ASSERT_TRUE(extension);
     first_extension_id_ = extension->id();
-    CheckExtensionConsistency(size_before);
+    CheckExtensionConsistency(first_extension_id_);
   }
 
   void LoadSecondExtension() {
-    int offset = GetExtensionService()->extensions()->size();
-    ASSERT_TRUE(LoadExtension(
-        test_data_dir_.AppendASCII("install").AppendASCII("install")));
-    const Extension* extension =
-        GetExtensionService()->extensions()->at(offset);
+    const Extension* extension = LoadExtension(
+        test_data_dir_.AppendASCII("install").AppendASCII("install"));
     ASSERT_TRUE(extension);
     second_extension_id_ = extension->id();
-    CheckExtensionConsistency(offset);
+    CheckExtensionConsistency(second_extension_id_);
   }
 
   std::string first_extension_id_;
@@ -129,14 +120,14 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest, Basic) {
   const size_t crash_size_before =
       GetExtensionService()->terminated_extensions()->size();
   LoadTestExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
   ASSERT_EQ(crash_size_before + 1,
             GetExtensionService()->terminated_extensions()->size());
   AcceptNotification(0);
 
   SCOPED_TRACE("after clicking the balloon");
-  CheckExtensionConsistency(size_before);
+  CheckExtensionConsistency(first_extension_id_);
   ASSERT_EQ(crash_size_before,
             GetExtensionService()->terminated_extensions()->size());
 }
@@ -146,7 +137,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest, CloseAndReload) {
   const size_t crash_size_before =
       GetExtensionService()->terminated_extensions()->size();
   LoadTestExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
 
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
   ASSERT_EQ(crash_size_before + 1,
@@ -156,7 +147,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest, CloseAndReload) {
   ReloadExtension(first_extension_id_);
 
   SCOPED_TRACE("after reloading");
-  CheckExtensionConsistency(size_before);
+  CheckExtensionConsistency(first_extension_id_);
   ASSERT_EQ(crash_size_before,
             GetExtensionService()->terminated_extensions()->size());
 }
@@ -164,13 +155,13 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest, CloseAndReload) {
 IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest, ReloadIndependently) {
   const size_t size_before = GetExtensionService()->extensions()->size();
   LoadTestExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
 
   ReloadExtension(first_extension_id_);
 
   SCOPED_TRACE("after reloading");
-  CheckExtensionConsistency(size_before);
+  CheckExtensionConsistency(first_extension_id_);
 
   TabContents* current_tab = browser()->GetSelectedTabContents();
   ASSERT_TRUE(current_tab);
@@ -184,7 +175,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
                        ReloadIndependentlyChangeTabs) {
   const size_t size_before = GetExtensionService()->extensions()->size();
   LoadTestExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
 
   TabContents* original_tab = browser()->GetSelectedTabContents();
@@ -201,7 +192,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
   ReloadExtension(first_extension_id_);
 
   SCOPED_TRACE("after reloading");
-  CheckExtensionConsistency(size_before);
+  CheckExtensionConsistency(first_extension_id_);
 
   // The balloon should automatically hide after the extension is successfully
   // reloaded.
@@ -212,7 +203,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
                        ReloadIndependentlyNavigatePage) {
   const size_t size_before = GetExtensionService()->extensions()->size();
   LoadTestExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
 
   TabContents* current_tab = browser()->GetSelectedTabContents();
@@ -228,7 +219,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
   ReloadExtension(first_extension_id_);
 
   SCOPED_TRACE("after reloading");
-  CheckExtensionConsistency(size_before);
+  CheckExtensionConsistency(first_extension_id_);
 
   // The balloon should automatically hide after the extension is successfully
   // reloaded.
@@ -249,7 +240,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
 IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest, MAYBE_ShutdownWhileCrashed) {
   const size_t size_before = GetExtensionService()->extensions()->size();
   LoadTestExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
 }
 
@@ -257,26 +248,26 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest, TwoExtensionsCrashFirst) {
   const size_t size_before = GetExtensionService()->extensions()->size();
   LoadTestExtension();
   LoadSecondExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before + 1, GetExtensionService()->extensions()->size());
   AcceptNotification(0);
 
   SCOPED_TRACE("after clicking the balloon");
-  CheckExtensionConsistency(size_before);
-  CheckExtensionConsistency(size_before + 1);
+  CheckExtensionConsistency(first_extension_id_);
+  CheckExtensionConsistency(second_extension_id_);
 }
 
 IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest, TwoExtensionsCrashSecond) {
   const size_t size_before = GetExtensionService()->extensions()->size();
   LoadTestExtension();
   LoadSecondExtension();
-  CrashExtension(size_before + 1);
+  CrashExtension(second_extension_id_);
   ASSERT_EQ(size_before + 1, GetExtensionService()->extensions()->size());
   AcceptNotification(0);
 
   SCOPED_TRACE("after clicking the balloon");
-  CheckExtensionConsistency(size_before);
-  CheckExtensionConsistency(size_before + 1);
+  CheckExtensionConsistency(first_extension_id_);
+  CheckExtensionConsistency(second_extension_id_);
 }
 
 IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
@@ -286,11 +277,11 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
       GetExtensionService()->terminated_extensions()->size();
   LoadTestExtension();
   LoadSecondExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before + 1, GetExtensionService()->extensions()->size());
   ASSERT_EQ(crash_size_before + 1,
             GetExtensionService()->terminated_extensions()->size());
-  CrashExtension(size_before);
+  CrashExtension(second_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
   ASSERT_EQ(crash_size_before + 2,
             GetExtensionService()->terminated_extensions()->size());
@@ -298,37 +289,37 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
   {
     SCOPED_TRACE("first balloon");
     AcceptNotification(0);
-    CheckExtensionConsistency(size_before);
+    CheckExtensionConsistency(first_extension_id_);
   }
 
   {
     SCOPED_TRACE("second balloon");
     AcceptNotification(0);
-    CheckExtensionConsistency(size_before);
-    CheckExtensionConsistency(size_before + 1);
+    CheckExtensionConsistency(first_extension_id_);
+    CheckExtensionConsistency(second_extension_id_);
   }
 }
 
 IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest, TwoExtensionsOneByOne) {
   const size_t size_before = GetExtensionService()->extensions()->size();
   LoadTestExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
   LoadSecondExtension();
-  CrashExtension(size_before);
+  CrashExtension(second_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
 
   {
     SCOPED_TRACE("first balloon");
     AcceptNotification(0);
-    CheckExtensionConsistency(size_before);
+    CheckExtensionConsistency(first_extension_id_);
   }
 
   {
     SCOPED_TRACE("second balloon");
     AcceptNotification(0);
-    CheckExtensionConsistency(size_before);
-    CheckExtensionConsistency(size_before + 1);
+    CheckExtensionConsistency(first_extension_id_);
+    CheckExtensionConsistency(second_extension_id_);
   }
 }
 
@@ -348,10 +339,10 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
                        MAYBE_TwoExtensionsShutdownWhileCrashed) {
   const size_t size_before = GetExtensionService()->extensions()->size();
   LoadTestExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
   LoadSecondExtension();
-  CrashExtension(size_before);
+  CrashExtension(second_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
 }
 
@@ -360,9 +351,9 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
   const size_t size_before = GetExtensionService()->extensions()->size();
   LoadTestExtension();
   LoadSecondExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before + 1, GetExtensionService()->extensions()->size());
-  CrashExtension(size_before);
+  CrashExtension(second_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
 
   // Accept notification 1 before canceling notification 0.
@@ -373,9 +364,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
 
   SCOPED_TRACE("balloons done");
   ASSERT_EQ(size_before + 1, GetExtensionService()->extensions()->size());
-  EXPECT_EQ(second_extension_id_,
-            GetExtensionService()->extensions()->at(size_before)->id());
-  CheckExtensionConsistency(size_before);
+  CheckExtensionConsistency(second_extension_id_);
 }
 
 IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
@@ -383,9 +372,9 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
   const size_t size_before = GetExtensionService()->extensions()->size();
   LoadTestExtension();
   LoadSecondExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before + 1, GetExtensionService()->extensions()->size());
-  CrashExtension(size_before);
+  CrashExtension(second_extension_id_);
   ASSERT_EQ(size_before, GetExtensionService()->extensions()->size());
 
   {
@@ -397,14 +386,14 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
     ReloadExtension(first_extension_id_);
     // One of the balloons should hide after the extension is reloaded.
     ASSERT_EQ(1U, CountBalloons());
-    CheckExtensionConsistency(size_before);
+    CheckExtensionConsistency(first_extension_id_);
   }
 
   {
     SCOPED_TRACE("second: balloon");
     AcceptNotification(0);
-    CheckExtensionConsistency(size_before);
-    CheckExtensionConsistency(size_before + 1);
+    CheckExtensionConsistency(first_extension_id_);
+    CheckExtensionConsistency(second_extension_id_);
   }
 }
 
@@ -414,7 +403,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest, CrashAndUninstall) {
       GetExtensionService()->terminated_extensions()->size();
   LoadTestExtension();
   LoadSecondExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before + 1, GetExtensionService()->extensions()->size());
   ASSERT_EQ(crash_size_before + 1,
             GetExtensionService()->terminated_extensions()->size());
@@ -443,7 +432,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest, MAYBE_CrashAndUnloadAll) {
       GetExtensionService()->terminated_extensions()->size();
   LoadTestExtension();
   LoadSecondExtension();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
   ASSERT_EQ(size_before + 1, GetExtensionService()->extensions()->size());
   ASSERT_EQ(crash_size_before + 1,
             GetExtensionService()->terminated_extensions()->size());
@@ -471,7 +460,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
       GURL("chrome-extension://" + first_extension_id_ + "/background.html"));
 
   const int tabs_before = tab_strip->count();
-  CrashExtension(size_before);
+  CrashExtension(first_extension_id_);
 
   // Tab should still be open, and extension should be crashed.
   EXPECT_EQ(tabs_before, tab_strip->count());
@@ -488,6 +477,8 @@ IN_PROC_BROWSER_TEST_F(ExtensionCrashRecoveryTest,
     observer.Wait();
   }
   // Extension should now be loaded.
+  SCOPED_TRACE("after reloading the tab");
+  CheckExtensionConsistency(first_extension_id_);
   ASSERT_EQ(size_before + 1, GetExtensionService()->extensions()->size());
   ASSERT_EQ(0U, CountBalloons());
 }
diff --git a/chrome/browser/extensions/extension_file_browser_private_api.cc b/chrome/browser/extensions/extension_file_browser_private_api.cc
index c6456c0..f529e06 100644
--- a/chrome/browser/extensions/extension_file_browser_private_api.cc
+++ b/chrome/browser/extensions/extension_file_browser_private_api.cc
@@ -130,10 +130,10 @@ bool GetFileBrowserHandlers(Profile* profile,
   if (!service)
     return false;  // In unit-tests, we may not have an ExtensionService.
 
-  for (ExtensionList::const_iterator iter = service->extensions()->begin();
+  for (ExtensionSet::const_iterator iter = service->extensions()->begin();
        iter != service->extensions()->end();
        ++iter) {
-    const Extension* extension = iter->get();
+    const Extension* extension = *iter;
     if (!extension->file_browser_handlers())
       continue;
 
diff --git a/chrome/browser/extensions/extension_info_map.cc b/chrome/browser/extensions/extension_info_map.cc
index fdbd66a..929e106 100644
--- a/chrome/browser/extensions/extension_info_map.cc
+++ b/chrome/browser/extensions/extension_info_map.cc
@@ -138,11 +138,11 @@ bool ExtensionInfoMap::SecurityOriginHasAPIPermission(
         process_map_.Contains(id, process_id);
   }
 
-  ExtensionSet::ExtensionMap::const_iterator i = extensions_.begin();
+  ExtensionSet::const_iterator i = extensions_.begin();
   for (; i != extensions_.end(); ++i) {
-    if (i->second->web_extent().MatchesSecurityOrigin(origin) &&
-        process_map_.Contains(i->first, process_id) &&
-        i->second->HasAPIPermission(permission)) {
+    if ((*i)->web_extent().MatchesSecurityOrigin(origin) &&
+        process_map_.Contains((*i)->id(), process_id) &&
+        (*i)->HasAPIPermission(permission)) {
       return true;
     }
   }
diff --git a/chrome/browser/extensions/extension_management_api.cc b/chrome/browser/extensions/extension_management_api.cc
index 361a4ae..15d67a2 100644
--- a/chrome/browser/extensions/extension_management_api.cc
+++ b/chrome/browser/extensions/extension_management_api.cc
@@ -123,10 +123,10 @@ static DictionaryValue* CreateExtensionInfo(const Extension& extension,
 }
 
 static void AddExtensionInfo(ListValue* list,
-                             const ExtensionList& extensions,
+                             const ExtensionSet& extensions,
                              bool enabled,
                              ExtensionPrefs* prefs) {
-  for (ExtensionList::const_iterator i = extensions.begin();
+  for (ExtensionSet::const_iterator i = extensions.begin();
        i != extensions.end(); ++i) {
     const Extension& extension = **i;
 
diff --git a/chrome/browser/extensions/extension_management_browsertest.cc b/chrome/browser/extensions/extension_management_browsertest.cc
index 221f347..08c90dc 100644
--- a/chrome/browser/extensions/extension_management_browsertest.cc
+++ b/chrome/browser/extensions/extension_management_browsertest.cc
@@ -314,7 +314,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionManagementTest, AutoUpdate) {
   ExtensionTestMessageListener listener1("v1 installed", false);
   ExtensionService* service = browser()->profile()->GetExtensionService();
   const size_t size_before = service->extensions()->size();
-  ASSERT_TRUE(service->disabled_extensions()->empty());
+  ASSERT_TRUE(service->disabled_extensions()->is_empty());
   const Extension* extension =
       InstallExtension(basedir.AppendASCII("v1.crx"), 1);
   ASSERT_TRUE(extension);
@@ -382,7 +382,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionManagementTest, ExternalUrlUpdate) {
                                      basedir.AppendASCII("v2.crx"));
 
   const size_t size_before = service->extensions()->size();
-  ASSERT_TRUE(service->disabled_extensions()->empty());
+  ASSERT_TRUE(service->disabled_extensions()->is_empty());
 
   PendingExtensionManager* pending_extension_manager =
       service->pending_extension_manager();
@@ -465,7 +465,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionManagementTest, ExternalPolicyRefresh) {
                                      basedir.AppendASCII("v2.crx"));
 
   const size_t size_before = service->extensions()->size();
-  ASSERT_TRUE(service->disabled_extensions()->empty());
+  ASSERT_TRUE(service->disabled_extensions()->is_empty());
 
   PrefService* prefs = browser()->profile()->GetPrefs();
   const ListValue* forcelist =
@@ -520,7 +520,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionManagementTest, PolicyOverridesUserInstall) {
   service->updater()->set_blacklist_checks_enabled(false);
   const size_t size_before = service->extensions()->size();
   FilePath basedir = test_data_dir_.AppendASCII("autoupdate");
-  ASSERT_TRUE(service->disabled_extensions()->empty());
+  ASSERT_TRUE(service->disabled_extensions()->is_empty());
 
   // Note: This interceptor gets requests on the IO thread.
   scoped_refptr<AutoUpdateInterceptor> interceptor(new AutoUpdateInterceptor());
@@ -581,7 +581,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionManagementTest, PolicyOverridesUserInstall) {
   ASSERT_TRUE(extension);
   EXPECT_EQ(Extension::INTERNAL, extension->location());
   EXPECT_TRUE(service->IsExtensionEnabled(kExtensionId));
-  EXPECT_TRUE(service->disabled_extensions()->empty());
+  EXPECT_TRUE(service->disabled_extensions()->is_empty());
 
   service->DisableExtension(kExtensionId);
   EXPECT_EQ(1u, service->disabled_extensions()->size());
@@ -604,5 +604,5 @@ IN_PROC_BROWSER_TEST_F(ExtensionManagementTest, PolicyOverridesUserInstall) {
   ASSERT_TRUE(extension);
   EXPECT_EQ(Extension::EXTERNAL_POLICY_DOWNLOAD, extension->location());
   EXPECT_TRUE(service->IsExtensionEnabled(kExtensionId));
-  EXPECT_TRUE(service->disabled_extensions()->empty());
+  EXPECT_TRUE(service->disabled_extensions()->is_empty());
 }
diff --git a/chrome/browser/extensions/extension_override_apitest.cc b/chrome/browser/extensions/extension_override_apitest.cc
index 518d333..778ec2e 100644
--- a/chrome/browser/extensions/extension_override_apitest.cc
+++ b/chrome/browser/extensions/extension_override_apitest.cc
@@ -114,15 +114,16 @@ IN_PROC_BROWSER_TEST_F(ExtensionOverrideTest, MAYBE_OverrideHistory) {
 
 // Regression test for http://crbug.com/41442.
 IN_PROC_BROWSER_TEST_F(ExtensionOverrideTest, ShouldNotCreateDuplicateEntries) {
-  ASSERT_TRUE(LoadExtension(test_data_dir_.AppendASCII("override/history")));
+  const Extension* extension =
+      LoadExtension(test_data_dir_.AppendASCII("override/history"));
+  ASSERT_TRUE(extension);
 
   // Simulate several LoadExtension() calls happening over the lifetime of
   // a preferences file without corresponding UnloadExtension() calls.
   for (size_t i = 0; i < 3; ++i) {
     ExtensionWebUI::RegisterChromeURLOverrides(
         browser()->profile(),
-        browser()->profile()->GetExtensionService()->extensions()->back()->
-            GetChromeURLOverrides());
+        extension->GetChromeURLOverrides());
   }
 
   ASSERT_TRUE(CheckHistoryOverridesContainsNoDupes());
@@ -160,8 +161,9 @@ IN_PROC_BROWSER_TEST_F(ExtensionOverrideTest, OverrideKeyboard) {
   }
 
   // Load the failing version.  This should take precedence.
-  ASSERT_TRUE(LoadExtension(
-      test_data_dir_.AppendASCII("override").AppendASCII("keyboard_fails")));
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("override").AppendASCII("keyboard_fails"));
+  ASSERT_TRUE(extension);
   {
     ResultCatcher catcher;
     NavigateToKeyboard();
@@ -169,9 +171,7 @@ IN_PROC_BROWSER_TEST_F(ExtensionOverrideTest, OverrideKeyboard) {
   }
 
   // Unload the failing version.  We should be back to passing now.
-  const ExtensionList *extensions =
-      browser()->profile()->GetExtensionService()->extensions();
-  UnloadExtension((*extensions->rbegin())->id());
+  UnloadExtension(extension->id());
   {
     ResultCatcher catcher;
     NavigateToKeyboard();
diff --git a/chrome/browser/extensions/extension_preference_api.cc b/chrome/browser/extensions/extension_preference_api.cc
index 31b3161..ffbfc80 100644
--- a/chrome/browser/extensions/extension_preference_api.cc
+++ b/chrome/browser/extensions/extension_preference_api.cc
@@ -316,8 +316,8 @@ void ExtensionPreferenceEventRouter::OnPrefChanged(
   ExtensionEventRouter* router = profile_->GetExtensionEventRouter();
   if (!router || !router->HasEventListener(event_name))
     return;
-  const ExtensionList* extensions = extension_service->extensions();
-  for (ExtensionList::const_iterator it = extensions->begin();
+  const ExtensionSet* extensions = extension_service->extensions();
+  for (ExtensionSet::const_iterator it = extensions->begin();
        it != extensions->end(); ++it) {
     std::string extension_id = (*it)->id();
     // TODO(bauerb): Only iterate over registered event listeners.
diff --git a/chrome/browser/extensions/extension_process_manager.cc b/chrome/browser/extensions/extension_process_manager.cc
index 4f60ea3..50e8536 100644
--- a/chrome/browser/extensions/extension_process_manager.cc
+++ b/chrome/browser/extensions/extension_process_manager.cc
@@ -74,8 +74,8 @@ static void CreateBackgroundHostForExtensionLoad(
 }
 
 static void CreateBackgroundHostsForProfileStartup(
-    ExtensionProcessManager* manager, const ExtensionList* extensions) {
-  for (ExtensionList::const_iterator extension = extensions->begin();
+    ExtensionProcessManager* manager, const ExtensionSet* extensions) {
+  for (ExtensionSet::const_iterator extension = extensions->begin();
        extension != extensions->end(); ++extension) {
     CreateBackgroundHostForExtensionLoad(manager, *extension);
   }
diff --git a/chrome/browser/extensions/extension_service.cc b/chrome/browser/extensions/extension_service.cc
index 0b78055..5da59ed 100644
--- a/chrome/browser/extensions/extension_service.cc
+++ b/chrome/browser/extensions/extension_service.cc
@@ -444,15 +444,15 @@ ExtensionService::ExtensionService(Profile* profile,
                               install_directory_.value().length(), 0, 500, 100);
 }
 
-const ExtensionList* ExtensionService::extensions() const {
+const ExtensionSet* ExtensionService::extensions() const {
   return &extensions_;
 }
 
-const ExtensionList* ExtensionService::disabled_extensions() const {
+const ExtensionSet* ExtensionService::disabled_extensions() const {
   return &disabled_extensions_;
 }
 
-const ExtensionList* ExtensionService::terminated_extensions() const {
+const ExtensionSet* ExtensionService::terminated_extensions() const {
   return &terminated_extensions_;
 }
 
@@ -766,14 +766,11 @@ bool ExtensionService::UninstallExtension(
 
 bool ExtensionService::IsExtensionEnabled(
     const std::string& extension_id) const {
-  const Extension* extension =
-      GetExtensionByIdInternal(extension_id, true, false, true);
-  if (extension)
+  if (extensions_.Contains(extension_id) ||
+      terminated_extensions_.Contains(extension_id))
     return true;
 
-  extension =
-      GetExtensionByIdInternal(extension_id, false, true, false);
-  if (extension)
+  if (disabled_extensions_.Contains(extension_id))
     return false;
 
   // If the extension hasn't been loaded yet, check the prefs for it. Assume
@@ -803,11 +800,8 @@ void ExtensionService::EnableExtension(const std::string& extension_id) {
     return;
 
   // Move it over to the enabled list.
-  extensions_.push_back(make_scoped_refptr(extension));
-  ExtensionList::iterator iter = std::find(disabled_extensions_.begin(),
-                                           disabled_extensions_.end(),
-                                           extension);
-  disabled_extensions_.erase(iter);
+  extensions_.Insert(make_scoped_refptr(extension));
+  disabled_extensions_.Remove(extension->id());
 
   // Make sure any browser action contained within it is not hidden.
   extension_prefs_->SetBrowserActionVisibility(extension, true);
@@ -837,18 +831,11 @@ void ExtensionService::DisableExtension(const std::string& extension_id) {
     return;
 
   // Move it over to the disabled list.
-  disabled_extensions_.push_back(make_scoped_refptr(extension));
-  ExtensionList::iterator iter = std::find(extensions_.begin(),
-                                           extensions_.end(),
-                                           extension);
-  if (iter != extensions_.end()) {
-    extensions_.erase(iter);
-  } else {
-    iter = std::find(terminated_extensions_.begin(),
-                     terminated_extensions_.end(),
-                     extension);
-    terminated_extensions_.erase(iter);
-  }
+  disabled_extensions_.Insert(make_scoped_refptr(extension));
+  if (extensions_.Contains(extension->id()))
+    extensions_.Remove(extension->id());
+  else
+    terminated_extensions_.Remove(extension->id());
 
   NotifyExtensionUnloaded(extension, extension_misc::UNLOAD_REASON_DISABLE);
 
@@ -1115,7 +1102,7 @@ void ExtensionService::UpdateExtensionBlacklist(
   extension_prefs_->UpdateBlacklist(blacklist_set);
   std::vector<std::string> to_be_removed;
   // Loop current extensions, unload installed extensions.
-  for (ExtensionList::const_iterator iter = extensions_.begin();
+  for (ExtensionSet::const_iterator iter = extensions_.begin();
        iter != extensions_.end(); ++iter) {
     const Extension* extension = (*iter);
     if (blacklist_set.find(extension->id()) != blacklist_set.end()) {
@@ -1158,7 +1145,7 @@ ExtensionUpdater* ExtensionService::updater() {
 void ExtensionService::CheckAdminBlacklist() {
   std::vector<std::string> to_be_removed;
   // Loop through extensions list, unload installed extensions.
-  for (ExtensionList::const_iterator iter = extensions_.begin();
+  for (ExtensionSet::const_iterator iter = extensions_.begin();
        iter != extensions_.end(); ++iter) {
     const Extension* extension = (*iter);
     if (!extension_prefs_->IsExtensionAllowedByPolicy(extension->id(),
@@ -1359,10 +1346,10 @@ SyncError ExtensionService::ProcessSyncChanges(
 }
 
 void ExtensionService::GetSyncDataListHelper(
-    const ExtensionList& extensions,
+    const ExtensionSet& extensions,
     const SyncBundle& bundle,
     std::vector<ExtensionSyncData>* sync_data_list) const {
-  for (ExtensionList::const_iterator it = extensions.begin();
+  for (ExtensionSet::const_iterator it = extensions.begin();
        it != extensions.end(); ++it) {
     const Extension& extension = **it;
     if (bundle.filter(extension) &&
@@ -1498,8 +1485,7 @@ void ExtensionService::SetIsIncognitoEnabled(
 
   extension_prefs_->SetIsIncognitoEnabled(extension_id, enabled);
 
-  bool extension_is_enabled = std::find(extensions_.begin(), extensions_.end(),
-                                        extension) != extensions_.end();
+  bool extension_is_enabled = extensions_.Contains(extension->id());
 
   // When we reload the extension the ID may be invalidated if we've passed it
   // by const ref everywhere. Make a copy to be safe.
@@ -1576,8 +1562,7 @@ void ExtensionService::SetAllowFileAccess(const Extension* extension,
 
   extension_prefs_->SetAllowFileAccess(extension->id(), allow);
 
-  bool extension_is_enabled = std::find(extensions_.begin(), extensions_.end(),
-                                        extension) != extensions_.end();
+  bool extension_is_enabled = extensions_.Contains(extension->id());
   if (extension_is_enabled)
     ReloadExtension(extension->id());
 }
@@ -1681,12 +1666,9 @@ void ExtensionService::IdentifyAlertableExtensions() {
   scoped_ptr<ExtensionGlobalError> global_error(
       new ExtensionGlobalError(AsWeakPtr()));
   bool needs_alert = false;
-  for (ExtensionList::const_iterator iter = extensions_.begin();
+  for (ExtensionSet::const_iterator iter = extensions_.begin();
        iter != extensions_.end(); ++iter) {
     const Extension* e = *iter;
-    if (!IsExtensionEnabled(e->id())) {
-      continue;
-    }
     if (Extension::IsExternalLocation(e->location())) {
       if (!extension_prefs_->IsExternalExtensionAcknowledged(e->id())) {
         global_error->AddExternalExtension(e->id());
@@ -1790,13 +1772,10 @@ void ExtensionService::UnloadExtension(
   // Clean up runtime data.
   extension_runtime_data_.erase(extension_id);
 
-  ExtensionList::iterator iter = std::find(disabled_extensions_.begin(),
-                                           disabled_extensions_.end(),
-                                           extension.get());
-  if (iter != disabled_extensions_.end()) {
+if (disabled_extensions_.Contains(extension->id())) {
     UnloadedExtensionInfo details(extension, reason);
     details.already_disabled = true;
-    disabled_extensions_.erase(iter);
+    disabled_extensions_.Remove(extension->id());
     content::NotificationService::current()->Notify(
         chrome::NOTIFICATION_EXTENSION_UNLOADED,
         content::Source<Profile>(profile_),
@@ -1808,10 +1787,8 @@ void ExtensionService::UnloadExtension(
     return;
   }
 
-  iter = std::find(extensions_.begin(), extensions_.end(), extension.get());
-
-  // Remove the extension from our list.
-  extensions_.erase(iter);
+// Remove the extension from our list.
+  extensions_.Remove(extension->id());
 
   NotifyExtensionUnloaded(extension.get(), reason);
 }
@@ -1820,10 +1797,9 @@ void ExtensionService::UnloadAllExtensions() {
   profile_->GetExtensionSpecialStoragePolicy()->
       RevokeRightsForAllExtensions();
 
-  extensions_.clear();
-  disabled_extensions_.clear();
-  terminated_extension_ids_.clear();
-  terminated_extensions_.clear();
+  extensions_.Clear();
+  disabled_extensions_.Clear();
+  terminated_extensions_.Clear();
   extension_runtime_data_.clear();
 
   // TODO(erikkay) should there be a notification for this?  We can't use
@@ -1907,10 +1883,10 @@ void ExtensionService::AddExtension(const Extension* extension) {
 
   bool disabled = extension_prefs_->IsExtensionDisabled(extension->id());
   if (disabled) {
-    disabled_extensions_.push_back(scoped_extension);
-    // TODO(aa): This seems dodgy. It seems that AddExtension() could get called
-    // with a disabled extension for other reasons other than that an update was
-    // disabled.
+    disabled_extensions_.Insert(scoped_extension);
+    // TODO(aa): This seems dodgy. AddExtension() could get called with a
+    // disabled extension for other reasons other than that an update was
+    // disabled, e.g. as in ExtensionManagementTest.InstallRequiresConfirm.
     content::NotificationService::current()->Notify(
         chrome::NOTIFICATION_EXTENSION_UPDATE_DISABLED,
         content::Source<Profile>(profile_),
@@ -1919,7 +1895,7 @@ void ExtensionService::AddExtension(const Extension* extension) {
     return;
   }
 
-  extensions_.push_back(scoped_extension);
+  extensions_.Insert(scoped_extension);
   SyncExtensionChangeIfNeeded(*extension);
   NotifyExtensionLoaded(extension);
   IdentifyAlertableExtensions();
@@ -2031,10 +2007,11 @@ void ExtensionService::InitializePermissions(const Extension* extension) {
 
 void ExtensionService::UpdateActiveExtensionsInCrashReporter() {
   std::set<std::string> extension_ids;
-  for (size_t i = 0; i < extensions_.size(); ++i) {
-    if (!extensions_[i]->is_theme() &&
-        extensions_[i]->location() != Extension::COMPONENT)
-      extension_ids.insert(extensions_[i]->id());
+  for (ExtensionSet::const_iterator iter = extensions_.begin();
+       iter != extensions_.end(); ++iter) {
+    const Extension* extension = *iter;
+    if (!extension->is_theme() && extension->location() != Extension::COMPONENT)
+      extension_ids.insert(extension->id());
   }
 
   child_process_logging::SetActiveExtensions(extension_ids);
@@ -2127,51 +2104,33 @@ const Extension* ExtensionService::GetExtensionByIdInternal(
     bool include_terminated) const {
   std::string lowercase_id = StringToLowerASCII(id);
   if (include_enabled) {
-    for (ExtensionList::const_iterator iter = extensions_.begin();
-        iter != extensions_.end(); ++iter) {
-      if ((*iter)->id() == lowercase_id)
-        return *iter;
-    }
+    const Extension* extension = extensions_.GetByID(lowercase_id);
+    if (extension)
+      return extension;
   }
   if (include_disabled) {
-    for (ExtensionList::const_iterator iter = disabled_extensions_.begin();
-        iter != disabled_extensions_.end(); ++iter) {
-      if ((*iter)->id() == lowercase_id)
-        return *iter;
-    }
+    const Extension* extension = disabled_extensions_.GetByID(lowercase_id);
+    if (extension)
+      return extension;
   }
   if (include_terminated) {
-    for (ExtensionList::const_iterator iter = terminated_extensions_.begin();
-        iter != terminated_extensions_.end(); ++iter) {
-      if ((*iter)->id() == lowercase_id)
-        return *iter;
-    }
+    const Extension* extension = terminated_extensions_.GetByID(lowercase_id);
+    if (extension)
+      return extension;
   }
   return NULL;
 }
 
 void ExtensionService::TrackTerminatedExtension(const Extension* extension) {
-  if (terminated_extension_ids_.insert(extension->id()).second)
-    terminated_extensions_.push_back(make_scoped_refptr(extension));
-
-  // TODO(yoz): Listen to navcontrollers for that extension. Is this a todo?
+  if (!terminated_extensions_.Contains(extension->id()))
+    terminated_extensions_.Insert(make_scoped_refptr(extension));
 
-  // TODO(yoz): make sure this is okay in *ALL* the listeners!
   UnloadExtension(extension->id(), extension_misc::UNLOAD_REASON_TERMINATE);
 }
 
 void ExtensionService::UntrackTerminatedExtension(const std::string& id) {
   std::string lowercase_id = StringToLowerASCII(id);
-  if (terminated_extension_ids_.erase(lowercase_id) <= 0)
-    return;
-
-  for (ExtensionList::iterator iter = terminated_extensions_.begin();
-       iter != terminated_extensions_.end(); ++iter) {
-    if ((*iter)->id() == lowercase_id) {
-      terminated_extensions_.erase(iter);
-      return;
-    }
-  }
+  terminated_extensions_.Remove(lowercase_id);
 }
 
 const Extension* ExtensionService::GetTerminatedExtension(
@@ -2194,18 +2153,22 @@ const Extension* ExtensionService::GetExtensionByURL(const GURL& url) {
 }
 
 const Extension* ExtensionService::GetExtensionByWebExtent(const GURL& url) {
-  for (size_t i = 0; i < extensions_.size(); ++i) {
-    if (extensions_[i]->web_extent().MatchesURL(url))
-      return extensions_[i];
+  // TODO(yoz): Should be ExtensionSet::GetByURL.
+  for (ExtensionSet::const_iterator iter = extensions_.begin();
+       iter != extensions_.end(); ++iter) {
+    if ((*iter)->web_extent().MatchesURL(url))
+      return *iter;
   }
   return NULL;
 }
 
 const Extension* ExtensionService::GetDisabledExtensionByWebExtent(
     const GURL& url) {
-  for (size_t i = 0; i < disabled_extensions_.size(); ++i) {
-    if (disabled_extensions_[i]->web_extent().MatchesURL(url))
-      return disabled_extensions_[i];
+  // TODO(yoz): Should be ExtensionSet::GetByURL.
+  for (ExtensionSet::const_iterator iter = disabled_extensions_.begin();
+       iter != disabled_extensions_.end(); ++iter) {
+    if ((*iter)->web_extent().MatchesURL(url))
+      return *iter;
   }
   return NULL;
 }
@@ -2226,9 +2189,11 @@ bool ExtensionService::ExtensionBindingsAllowed(const GURL& url) {
 
 const Extension* ExtensionService::GetExtensionByOverlappingWebExtent(
     const URLPatternSet& extent) {
-  for (size_t i = 0; i < extensions_.size(); ++i) {
-    if (extensions_[i]->web_extent().OverlapsWith(extent))
-      return extensions_[i];
+  // TODO(yoz): Should be in ExtensionSet.
+  for (ExtensionSet::const_iterator iter = extensions_.begin();
+       iter != extensions_.end(); ++iter) {
+    if ((*iter)->web_extent().OverlapsWith(extent))
+      return *iter;
   }
 
   return NULL;
@@ -2370,9 +2335,9 @@ void ExtensionService::Observe(int type,
 
       // Loaded extensions.
       std::vector<ExtensionMsg_Loaded_Params> loaded_extensions;
-      for (size_t i = 0; i < extensions_.size(); ++i) {
-        loaded_extensions.push_back(
-            ExtensionMsg_Loaded_Params(extensions_[i]));
+      for (ExtensionSet::const_iterator iter = extensions_.begin();
+           iter != extensions_.end(); ++iter) {
+        loaded_extensions.push_back(ExtensionMsg_Loaded_Params(*iter));
       }
       process->Send(new ExtensionMsg_Loaded(loaded_extensions));
       break;
@@ -2423,7 +2388,7 @@ bool ExtensionService::HasApps() const {
 
 ExtensionIdSet ExtensionService::GetAppIds() const {
   ExtensionIdSet result;
-  for (ExtensionList::const_iterator it = extensions_.begin();
+  for (ExtensionSet::const_iterator it = extensions_.begin();
        it != extensions_.end(); ++it) {
     if ((*it)->is_app() && (*it)->location() != Extension::COMPONENT)
       result.insert((*it)->id());
diff --git a/chrome/browser/extensions/extension_service.h b/chrome/browser/extensions/extension_service.h
index 370ad22..67b0f4d 100644
--- a/chrome/browser/extensions/extension_service.h
+++ b/chrome/browser/extensions/extension_service.h
@@ -41,6 +41,7 @@
 #include "chrome/browser/sync/api/syncable_service.h"
 #include "chrome/common/extensions/extension.h"
 #include "chrome/common/extensions/extension_constants.h"
+#include "chrome/common/extensions/extension_set.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
@@ -86,7 +87,7 @@ class ExtensionServiceInterface : public SyncableService {
   typedef bool (*ExtensionFilter)(const Extension&);
 
   virtual ~ExtensionServiceInterface() {}
-  virtual const ExtensionList* extensions() const = 0;
+  virtual const ExtensionSet* extensions() const = 0;
   virtual PendingExtensionManager* pending_extension_manager() = 0;
 
   // Install an update.  Return true if the install can be started.
@@ -192,9 +193,9 @@ class ExtensionService
   virtual ~ExtensionService();
 
   // Gets the list of currently installed extensions.
-  virtual const ExtensionList* extensions() const OVERRIDE;
-  const ExtensionList* disabled_extensions() const;
-  const ExtensionList* terminated_extensions() const;
+  virtual const ExtensionSet* extensions() const OVERRIDE;
+  const ExtensionSet* disabled_extensions() const;
+  const ExtensionSet* terminated_extensions() const;
 
   // Gets the object managing the set of pending extensions.
   virtual PendingExtensionManager* pending_extension_manager() OVERRIDE;
@@ -635,7 +636,7 @@ class ExtensionService
   // Appends sync data objects for every extension in |extensions|
   // that passes |filter|.
   void GetSyncDataListHelper(
-      const ExtensionList& extensions,
+      const ExtensionSet& extensions,
       const SyncBundle& bundle,
       std::vector<ExtensionSyncData>* sync_data_list) const;
 
@@ -695,16 +696,13 @@ class ExtensionService
 
   // The current list of installed extensions.
   // TODO(aa): This should use chrome/common/extensions/extension_set.h.
-  ExtensionList extensions_;
+  ExtensionSet extensions_;
 
   // The list of installed extensions that have been disabled.
-  ExtensionList disabled_extensions_;
+  ExtensionSet disabled_extensions_;
 
   // The list of installed extensions that have been terminated.
-  ExtensionList terminated_extensions_;
-
-  // Used to quickly check if an extension was terminated.
-  std::set<std::string> terminated_extension_ids_;
+  ExtensionSet terminated_extensions_;
 
   // Hold the set of pending extensions.
   PendingExtensionManager pending_extension_manager_;
diff --git a/chrome/browser/extensions/extension_service_unittest.cc b/chrome/browser/extensions/extension_service_unittest.cc
index 78ef149..eaee17a 100644
--- a/chrome/browser/extensions/extension_service_unittest.cc
+++ b/chrome/browser/extensions/extension_service_unittest.cc
@@ -1875,7 +1875,7 @@ TEST_F(ExtensionServiceTest, UpdateApps) {
 TEST_F(ExtensionServiceTest, InstallAppsWithUnlimitedStorage) {
   InitializeEmptyExtensionService();
   InitializeRequestContext();
-  EXPECT_TRUE(service_->extensions()->empty());
+  EXPECT_TRUE(service_->extensions()->is_empty());
 
   int pref_count = 0;
 
@@ -1926,7 +1926,7 @@ TEST_F(ExtensionServiceTest, InstallAppsWithUnlimitedStorage) {
 TEST_F(ExtensionServiceTest, InstallAppsAndCheckStorageProtection) {
   InitializeEmptyExtensionService();
   InitializeRequestContext();
-  EXPECT_TRUE(service_->extensions()->empty());
+  EXPECT_TRUE(service_->extensions()->is_empty());
 
   int pref_count = 0;
 
@@ -1955,7 +1955,7 @@ TEST_F(ExtensionServiceTest, InstallAppsAndCheckStorageProtection) {
 
   UninstallExtension(id2, false);
 
-  EXPECT_TRUE(service_->extensions()->empty());
+  EXPECT_TRUE(service_->extensions()->is_empty());
   EXPECT_FALSE(profile_->GetExtensionSpecialStoragePolicy()->
       IsStorageProtected(origin1));
   EXPECT_FALSE(profile_->GetExtensionSpecialStoragePolicy()->
@@ -2676,18 +2676,18 @@ TEST_F(ExtensionServiceTest, DisableExtension) {
   InitializeEmptyExtensionService();
 
   InstallCRX(data_dir_.AppendASCII("good.crx"), INSTALL_NEW);
-  EXPECT_FALSE(service_->extensions()->empty());
+  EXPECT_FALSE(service_->extensions()->is_empty());
   EXPECT_TRUE(service_->GetExtensionById(good_crx, true));
   EXPECT_TRUE(service_->GetExtensionById(good_crx, false));
-  EXPECT_TRUE(service_->disabled_extensions()->empty());
+  EXPECT_TRUE(service_->disabled_extensions()->is_empty());
 
   // Disable it.
   service_->DisableExtension(good_crx);
 
-  EXPECT_TRUE(service_->extensions()->empty());
+  EXPECT_TRUE(service_->extensions()->is_empty());
   EXPECT_TRUE(service_->GetExtensionById(good_crx, true));
   EXPECT_FALSE(service_->GetExtensionById(good_crx, false));
-  EXPECT_FALSE(service_->disabled_extensions()->empty());
+  EXPECT_FALSE(service_->disabled_extensions()->is_empty());
 }
 
 TEST_F(ExtensionServiceTest, DisableTerminatedExtension) {
@@ -2702,7 +2702,7 @@ TEST_F(ExtensionServiceTest, DisableTerminatedExtension) {
 
   EXPECT_FALSE(service_->GetTerminatedExtension(good_crx));
   EXPECT_TRUE(service_->GetExtensionById(good_crx, true));
-  EXPECT_FALSE(service_->disabled_extensions()->empty());
+  EXPECT_FALSE(service_->disabled_extensions()->is_empty());
 }
 
 // Tests disabling all extensions (simulating --disable-extensions flag).
diff --git a/chrome/browser/extensions/extension_startup_browsertest.cc b/chrome/browser/extensions/extension_startup_browsertest.cc
index 835d274..20234e6 100644
--- a/chrome/browser/extensions/extension_startup_browsertest.cc
+++ b/chrome/browser/extensions/extension_startup_browsertest.cc
@@ -83,8 +83,9 @@ class ExtensionStartupTestBase : public InProcessBrowserTest {
 
     // Count the number of non-component extensions.
     int found_extensions = 0;
-    for (size_t i = 0; i < service->extensions()->size(); i++)
-      if (service->extensions()->at(i)->location() != Extension::COMPONENT)
+    for (ExtensionSet::const_iterator it = service->extensions()->begin();
+         it != service->extensions()->end(); ++it)
+      if ((*it)->location() != Extension::COMPONENT)
         found_extensions++;
 
     ASSERT_EQ(static_cast<uint32>(num_expected_extensions),
@@ -163,17 +164,25 @@ IN_PROC_BROWSER_TEST_F(ExtensionsStartupTest, Test) {
 IN_PROC_BROWSER_TEST_F(ExtensionsStartupTest, MAYBE_NoFileAccess) {
   WaitForServicesToStart(num_expected_extensions_, true);
 
+  // Keep a separate list of extensions for which to disable file access, since
+  // doing so reloads them.
+  std::vector<const Extension*> extension_list;
+
   ExtensionService* service = browser()->profile()->GetExtensionService();
-  for (size_t i = 0; i < service->extensions()->size(); ++i) {
-    if (service->extensions()->at(i)->location() == Extension::COMPONENT)
+  for (ExtensionSet::const_iterator it = service->extensions()->begin();
+       it != service->extensions()->end(); ++it) {
+    if ((*it)->location() == Extension::COMPONENT)
       continue;
-    if (service->AllowFileAccess(service->extensions()->at(i))) {
-      ui_test_utils::WindowedNotificationObserver user_scripts_observer(
-          chrome::NOTIFICATION_USER_SCRIPTS_UPDATED,
-          content::NotificationService::AllSources());
-      service->SetAllowFileAccess(service->extensions()->at(i), false);
-      user_scripts_observer.Wait();
-    }
+    if (service->AllowFileAccess(*it))
+      extension_list.push_back(*it);
+  }
+
+  for (size_t i = 0; i < extension_list.size(); ++i) {
+    ui_test_utils::WindowedNotificationObserver user_scripts_observer(
+        chrome::NOTIFICATION_USER_SCRIPTS_UPDATED,
+        content::NotificationService::AllSources());
+    service->SetAllowFileAccess(extension_list[i], false);
+    user_scripts_observer.Wait();
   }
 
   TestInjection(false, false);
diff --git a/chrome/browser/extensions/extension_tab_helper.cc b/chrome/browser/extensions/extension_tab_helper.cc
index 1853360..7fe6986 100644
--- a/chrome/browser/extensions/extension_tab_helper.cc
+++ b/chrome/browser/extensions/extension_tab_helper.cc
@@ -98,9 +98,9 @@ void ExtensionTabHelper::DidNavigateMainFrame(
   if (!service)
     return;
 
-  for (size_t i = 0; i < service->extensions()->size(); ++i) {
-    ExtensionAction* browser_action =
-        service->extensions()->at(i)->browser_action();
+  for (ExtensionSet::const_iterator it = service->extensions()->begin();
+       it != service->extensions()->end(); ++it) {
+    ExtensionAction* browser_action = (*it)->browser_action();
     if (browser_action) {
       browser_action->ClearAllValuesForTab(
           wrapper_->restore_tab_helper()->session_id().id());
@@ -110,8 +110,7 @@ void ExtensionTabHelper::DidNavigateMainFrame(
           content::NotificationService::NoDetails());
     }
 
-    ExtensionAction* page_action =
-        service->extensions()->at(i)->page_action();
+    ExtensionAction* page_action = (*it)->page_action();
     if (page_action) {
       page_action->ClearAllValuesForTab(
           wrapper_->restore_tab_helper()->session_id().id());
diff --git a/chrome/browser/extensions/extension_toolbar_model.cc b/chrome/browser/extensions/extension_toolbar_model.cc
index 6f8c695..24f9629 100644
--- a/chrome/browser/extensions/extension_toolbar_model.cc
+++ b/chrome/browser/extensions/extension_toolbar_model.cc
@@ -181,8 +181,9 @@ void ExtensionToolbarModel::InitializeExtensionList() {
   ExtensionList unsorted;
 
   // Create the lists.
-  for (size_t i = 0; i < service_->extensions()->size(); ++i) {
-    const Extension* extension = service_->extensions()->at(i);
+  for (ExtensionSet::const_iterator it = service_->extensions()->begin();
+       it != service_->extensions()->end(); ++it) {
+    const Extension* extension = *it;
     if (!extension->browser_action())
       continue;
     if (!service_->GetBrowserActionVisibility(extension))
diff --git a/chrome/browser/extensions/extension_tts_engine_api.cc b/chrome/browser/extensions/extension_tts_engine_api.cc
index 5eb86b9..db0d6fe 100644
--- a/chrome/browser/extensions/extension_tts_engine_api.cc
+++ b/chrome/browser/extensions/extension_tts_engine_api.cc
@@ -28,8 +28,8 @@ void GetExtensionVoices(Profile* profile, ListValue* result_voices) {
   ExtensionEventRouter* event_router = profile->GetExtensionEventRouter();
   DCHECK(event_router);
 
-  const ExtensionList* extensions = service->extensions();
-  ExtensionList::const_iterator iter;
+  const ExtensionSet* extensions = service->extensions();
+  ExtensionSet::const_iterator iter;
   for (iter = extensions->begin(); iter != extensions->end(); ++iter) {
     const Extension* extension = *iter;
 
@@ -93,8 +93,8 @@ bool GetMatchingExtensionVoice(
 
   *matching_extension = NULL;
   *voice_index = -1;
-  const ExtensionList* extensions = service->extensions();
-  ExtensionList::const_iterator iter;
+  const ExtensionSet* extensions = service->extensions();
+  ExtensionSet::const_iterator iter;
   for (iter = extensions->begin(); iter != extensions->end(); ++iter) {
     const Extension* extension = *iter;
 
diff --git a/chrome/browser/extensions/extension_updater.cc b/chrome/browser/extensions/extension_updater.cc
index ff1b8ce..2048d9f 100644
--- a/chrome/browser/extensions/extension_updater.cc
+++ b/chrome/browser/extensions/extension_updater.cc
@@ -1025,8 +1025,8 @@ void ExtensionUpdater::CheckNow() {
     }
   }
 
-  const ExtensionList* extensions = service_->extensions();
-  for (ExtensionList::const_iterator iter = extensions->begin();
+  const ExtensionSet* extensions = service_->extensions();
+  for (ExtensionSet::const_iterator iter = extensions->begin();
        iter != extensions->end(); ++iter) {
     // An extension might be overwritten by policy, and have its update url
     // changed. Make sure existing extensions aren't fetched again, if a
diff --git a/chrome/browser/extensions/extension_updater_unittest.cc b/chrome/browser/extensions/extension_updater_unittest.cc
index e8f3c52..e475feb 100644
--- a/chrome/browser/extensions/extension_updater_unittest.cc
+++ b/chrome/browser/extensions/extension_updater_unittest.cc
@@ -153,16 +153,10 @@ class ServiceForManifestTests : public MockService {
 
   virtual const Extension* GetExtensionById(
       const std::string& id, bool include_disabled) const OVERRIDE {
-    for (ExtensionList::const_iterator iter = extensions_.begin();
-        iter != extensions_.end(); ++iter) {
-      if ((*iter)->id() == id) {
-        return *iter;
-      }
-    }
-    return NULL;
+    return extensions_.GetByID(id);
   }
 
-  virtual const ExtensionList* extensions() const OVERRIDE {
+  virtual const ExtensionSet* extensions() const OVERRIDE {
     return &extensions_;
   }
 
@@ -171,11 +165,14 @@ class ServiceForManifestTests : public MockService {
   }
 
   void set_extensions(ExtensionList extensions) {
-    extensions_ = extensions;
+    for (ExtensionList::const_iterator it = extensions.begin();
+         it != extensions.end(); ++it) {
+      extensions_.Insert(*it);
+    }
   }
 
  private:
-  ExtensionList extensions_;
+  ExtensionSet extensions_;
 };
 
 class ServiceForDownloadTests : public MockService {
diff --git a/chrome/browser/extensions/extension_webrequest_api.cc b/chrome/browser/extensions/extension_webrequest_api.cc
index 21fdce9..481c015 100644
--- a/chrome/browser/extensions/extension_webrequest_api.cc
+++ b/chrome/browser/extensions/extension_webrequest_api.cc
@@ -1697,9 +1697,9 @@ void SendExtensionWebRequestStatusToHost(content::RenderProcessHost* host) {
   bool adblock = false;
   bool adblock_plus = false;
   bool other = false;
-  const ExtensionList* extensions =
+  const ExtensionSet* extensions =
       profile->GetExtensionService()->extensions();
-  for (ExtensionList::const_iterator it = extensions->begin();
+  for (ExtensionSet::const_iterator it = extensions->begin();
        it != extensions->end(); ++it) {
     if (profile->GetExtensionService()->HasUsedWebRequest(*it)) {
       if ((*it)->name().find("Adblock Plus") != std::string::npos) {
diff --git a/chrome/browser/extensions/installed_loader.cc b/chrome/browser/extensions/installed_loader.cc
index 2fb5e2d..d74bff4 100644
--- a/chrome/browser/extensions/installed_loader.cc
+++ b/chrome/browser/extensions/installed_loader.cc
@@ -181,8 +181,8 @@ void InstalledLoader::LoadAllExtensions() {
   int theme_count = 0;
   int page_action_count = 0;
   int browser_action_count = 0;
-  const ExtensionList* extensions = extension_service_->extensions();
-  ExtensionList::const_iterator ex;
+  const ExtensionSet* extensions = extension_service_->extensions();
+  ExtensionSet::const_iterator ex;
   for (ex = extensions->begin(); ex != extensions->end(); ++ex) {
     Extension::Location location = (*ex)->location();
     Extension::Type type = (*ex)->GetType();
@@ -246,7 +246,7 @@ void InstalledLoader::LoadAllExtensions() {
       ++browser_action_count;
 
     extension_service_->RecordPermissionMessagesHistogram(
-        ex->get(), "Extensions.Permissions_Load");
+        *ex, "Extensions.Permissions_Load");
   }
   UMA_HISTOGRAM_COUNTS_100("Extensions.LoadApp",
                            app_user_count + app_external_count);
diff --git a/chrome/browser/extensions/network_delay_listener_unittest.cc b/chrome/browser/extensions/network_delay_listener_unittest.cc
index 4e48472..e9d8f58 100644
--- a/chrome/browser/extensions/network_delay_listener_unittest.cc
+++ b/chrome/browser/extensions/network_delay_listener_unittest.cc
@@ -127,9 +127,9 @@ class NetworkDelayListenerTest
 
   void LoadTestExtension1() {
     LoadTestExtension(kTestExtensionId1);
-    ASSERT_FALSE(service_->extensions()->empty());
-    extension1_ = service_->extensions()->at(0).get();
-    ASSERT_FALSE(extension1_ == NULL);
+    ASSERT_FALSE(service_->extensions()->is_empty());
+    extension1_ = service_->extensions()->GetByID(kTestExtensionId1);
+    ASSERT_TRUE(extension1_);
   }
 
   void SendExtensionLoadedNotification(const Extension* extension) {
@@ -197,8 +197,9 @@ TEST_F(NetworkDelayListenerTest, TwoBlockingExtensions) {
   LoadTestExtension1();
   LoadTestExtension(kTestExtensionId2);
   ASSERT_EQ(2u, service_->extensions()->size());
-  const Extension* extension2 = service_->extensions()->at(1).get();
-  ASSERT_FALSE(extension2 == NULL);
+  const Extension* extension2 =
+      service_->extensions()->GetByID(kTestExtensionId2);
+  ASSERT_TRUE(extension2);
 
   TestDelegate delegate;
   scoped_ptr<TestURLRequest> request(StartTestRequest(&delegate, kTestUrl));
@@ -231,7 +232,7 @@ TEST_F(NetworkDelayListenerTest, ExtensionReadyTwice) {
 // Tests that there's no delay if no loaded extension needs one.
 TEST_F(NetworkDelayListenerTest, NoDelayNoWebRequest) {
   LoadTestExtension(kTestExtensionNoNetworkDelay);
-  ASSERT_FALSE(service_->extensions()->empty());
+  ASSERT_FALSE(service_->extensions()->is_empty());
 
   TestDelegate delegate;
   scoped_ptr<TestURLRequest> request(StartTestRequest(&delegate, kTestUrl));
diff --git a/chrome/browser/extensions/test_extension_service.cc b/chrome/browser/extensions/test_extension_service.cc
index 9e0be6e..e21ec88 100644
--- a/chrome/browser/extensions/test_extension_service.cc
+++ b/chrome/browser/extensions/test_extension_service.cc
@@ -9,7 +9,7 @@
 
 TestExtensionService::~TestExtensionService() {}
 
-const ExtensionList* TestExtensionService::extensions() const {
+const ExtensionSet* TestExtensionService::extensions() const {
   ADD_FAILURE();
   return NULL;
 }
diff --git a/chrome/browser/extensions/test_extension_service.h b/chrome/browser/extensions/test_extension_service.h
index 2e7d2e4..fa3ee0d 100644
--- a/chrome/browser/extensions/test_extension_service.h
+++ b/chrome/browser/extensions/test_extension_service.h
@@ -21,7 +21,7 @@ class TestExtensionService : public ExtensionServiceInterface {
   virtual ~TestExtensionService();
 
   // ExtensionServiceInterface implementation.
-  virtual const ExtensionList* extensions() const OVERRIDE;
+  virtual const ExtensionSet* extensions() const OVERRIDE;
   virtual PendingExtensionManager* pending_extension_manager() OVERRIDE;
 
   virtual bool UpdateExtension(
diff --git a/chrome/browser/extensions/unpacked_installer.cc b/chrome/browser/extensions/unpacked_installer.cc
index eccf275..9bbea9a 100644
--- a/chrome/browser/extensions/unpacked_installer.cc
+++ b/chrome/browser/extensions/unpacked_installer.cc
@@ -194,15 +194,12 @@ void UnpackedInstaller::OnLoaded(
   CHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   if (!service_weak_.get())
     return;
-  const ExtensionList* disabled_extensions =
+  const ExtensionSet* disabled_extensions =
       service_weak_->disabled_extensions();
   if (service_weak_->show_extensions_prompts() &&
       prompt_for_plugins_ &&
       !extension->plugins().empty() &&
-      std::find(disabled_extensions->begin(),
-                disabled_extensions->end(),
-                extension) !=
-      disabled_extensions->end()) {
+      disabled_extensions->Contains(extension->id())) {
     SimpleExtensionLoadPrompt* prompt = new SimpleExtensionLoadPrompt(
         service_weak_->profile(),
         service_weak_,
diff --git a/chrome/browser/extensions/user_script_listener.cc b/chrome/browser/extensions/user_script_listener.cc
index 5a54e20..b169f12 100644
--- a/chrome/browser/extensions/user_script_listener.cc
+++ b/chrome/browser/extensions/user_script_listener.cc
@@ -200,7 +200,7 @@ void UserScriptListener::Observe(int type,
       // Clear all our patterns and reregister all the still-loaded extensions.
       URLPatterns new_patterns;
       ExtensionService* service = profile->GetExtensionService();
-      for (ExtensionList::const_iterator it = service->extensions()->begin();
+      for (ExtensionSet::const_iterator it = service->extensions()->begin();
            it != service->extensions()->end(); ++it) {
         if (*it != unloaded_extension)
           CollectURLPatterns(*it, &new_patterns);
diff --git a/chrome/browser/extensions/user_script_listener_unittest.cc b/chrome/browser/extensions/user_script_listener_unittest.cc
index f28c8d8..cbba08a 100644
--- a/chrome/browser/extensions/user_script_listener_unittest.cc
+++ b/chrome/browser/extensions/user_script_listener_unittest.cc
@@ -138,8 +138,8 @@ class UserScriptListenerTest
   }
 
   void UnloadTestExtension() {
-    ASSERT_FALSE(service_->extensions()->empty());
-    service_->UnloadExtension(service_->extensions()->at(0)->id(),
+    ASSERT_FALSE(service_->extensions()->is_empty());
+    service_->UnloadExtension((*service_->extensions()->begin())->id(),
                               extension_misc::UNLOAD_REASON_DISABLE);
   }
 
diff --git a/chrome/browser/intents/web_intents_registry.cc b/chrome/browser/intents/web_intents_registry.cc
index 4e35219..5a8a567 100644
--- a/chrome/browser/intents/web_intents_registry.cc
+++ b/chrome/browser/intents/web_intents_registry.cc
@@ -81,9 +81,9 @@ void WebIntentsRegistry::OnWebDataServiceRequestDone(
 
   // Loop over all intents in all extensions, collect ones matching the query.
   if (extension_service_) {
-    const ExtensionList* extensions = extension_service_->extensions();
+    const ExtensionSet* extensions = extension_service_->extensions();
     if (extensions) {
-      for (ExtensionList::const_iterator i(extensions->begin());
+      for (ExtensionSet::const_iterator i(extensions->begin());
            i != extensions->end(); ++i) {
         const IntentServiceList& intents((*i)->intents_services());
         for (IntentServiceList::const_iterator j(intents.begin());
diff --git a/chrome/browser/intents/web_intents_registry_unittest.cc b/chrome/browser/intents/web_intents_registry_unittest.cc
index f6b20db..f25b802 100644
--- a/chrome/browser/intents/web_intents_registry_unittest.cc
+++ b/chrome/browser/intents/web_intents_registry_unittest.cc
@@ -11,6 +11,7 @@
 #include "chrome/browser/intents/web_intents_registry.h"
 #include "chrome/browser/webdata/web_data_service.h"
 #include "chrome/common/chrome_paths.h"
+#include "chrome/common/extensions/extension_set.h"
 #include "content/test/test_browser_thread.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -21,49 +22,41 @@ using webkit_glue::WebIntentServiceData;
 class MockExtensionService: public TestExtensionService {
  public:
   virtual ~MockExtensionService() {}
-  MOCK_CONST_METHOD0(extensions, const ExtensionList*());
+  MOCK_CONST_METHOD0(extensions, const ExtensionSet*());
 };
 
+namespace {
+
 // TODO(groby): Unify loading functions with extension_manifest_unittest code.
-DictionaryValue* LoadManifestFile(const std::string& filename,
+DictionaryValue* LoadManifestFile(const FilePath& path,
                                   std::string* error) {
-  FilePath path;
-  PathService::Get(chrome::DIR_TEST_DATA, &path);
-  path = path.AppendASCII("extensions")
-      .AppendASCII("manifest_tests")
-      .AppendASCII(filename.c_str());
   EXPECT_TRUE(file_util::PathExists(path));
-
   JSONFileValueSerializer serializer(path);
   return static_cast<DictionaryValue*>(serializer.Deserialize(NULL, error));
 }
 
-namespace {
-
 scoped_refptr<Extension> LoadExtensionWithLocation(
-    DictionaryValue* value,
+    const std::string& name,
     Extension::Location location,
     bool strict_error_checks,
     std::string* error) {
   FilePath path;
   PathService::Get(chrome::DIR_TEST_DATA, &path);
-  path = path.AppendASCII("extensions").AppendASCII("manifest_tests");
+  path = path.AppendASCII("extensions")
+      .AppendASCII("manifest_tests")
+      .AppendASCII(name.c_str());
+  scoped_ptr<DictionaryValue> value(LoadManifestFile(path, error));
+  if (!value.get())
+    return NULL;
   int flags = Extension::NO_FLAGS;
   if (strict_error_checks)
     flags |= Extension::STRICT_ERROR_CHECKS;
-  return Extension::Create(path.DirName(), location, *value, flags, error);
-}
-
-scoped_refptr<Extension> LoadExtensionWithLocation(
-    const std::string& name,
-    Extension::Location location,
-    bool strict_error_checks,
-    std::string* error) {
-  scoped_ptr<DictionaryValue> value(LoadManifestFile(name, error));
-  if (!value.get())
-    return NULL;
-  return LoadExtensionWithLocation(value.get(), location,
-                                   strict_error_checks, error);
+  return Extension::CreateWithId(path.DirName(),
+                                 location,
+                                 *value,
+                                 flags,
+                                 Extension::GenerateIdForPath(path),
+                                 error);
 }
 
 scoped_refptr<Extension> LoadExtension(const std::string& name,
@@ -114,7 +107,7 @@ class WebIntentsRegistryTest : public testing::Test {
   content::TestBrowserThread db_thread_;
   scoped_refptr<WebDataService> wds_;
   MockExtensionService extension_service_;
-  ExtensionList extensions_;
+  ExtensionSet extensions_;
   WebIntentsRegistry registry_;
   ScopedTempDir temp_dir_;
 };
@@ -213,8 +206,9 @@ TEST_F(WebIntentsRegistryTest, GetAllIntents) {
 }
 
 TEST_F(WebIntentsRegistryTest, GetExtensionIntents) {
-  extensions_.push_back(LoadAndExpectSuccess("intent_valid.json"));
-  extensions_.push_back(LoadAndExpectSuccess("intent_valid_2.json"));
+  extensions_.Insert(LoadAndExpectSuccess("intent_valid.json"));
+  extensions_.Insert(LoadAndExpectSuccess("intent_valid_2.json"));
+  ASSERT_EQ(2U, extensions_.size());
 
   TestConsumer consumer;
   consumer.expected_id_ = registry_.GetAllIntentProviders(&consumer);
@@ -223,8 +217,9 @@ TEST_F(WebIntentsRegistryTest, GetExtensionIntents) {
 }
 
 TEST_F(WebIntentsRegistryTest, GetSomeExtensionIntents) {
-  extensions_.push_back(LoadAndExpectSuccess("intent_valid.json"));
-  extensions_.push_back(LoadAndExpectSuccess("intent_valid_2.json"));
+  extensions_.Insert(LoadAndExpectSuccess("intent_valid.json"));
+  extensions_.Insert(LoadAndExpectSuccess("intent_valid_2.json"));
+  ASSERT_EQ(2U, extensions_.size());
 
   TestConsumer consumer;
   consumer.expected_id_ = registry_.GetIntentProviders(
@@ -235,8 +230,9 @@ TEST_F(WebIntentsRegistryTest, GetSomeExtensionIntents) {
 }
 
 TEST_F(WebIntentsRegistryTest, GetIntentsFromMixedSources) {
-  extensions_.push_back(LoadAndExpectSuccess("intent_valid.json"));
-  extensions_.push_back(LoadAndExpectSuccess("intent_valid_2.json"));
+  extensions_.Insert(LoadAndExpectSuccess("intent_valid.json"));
+  extensions_.Insert(LoadAndExpectSuccess("intent_valid_2.json"));
+  ASSERT_EQ(2U, extensions_.size());
 
   webkit_glue::WebIntentServiceData service;
   service.service_url = GURL("http://somewhere.com/intent/edit.html");
diff --git a/chrome/browser/sync/test/integration/sync_extension_helper.cc b/chrome/browser/sync/test/integration/sync_extension_helper.cc
index be0d08b..08d1e8b 100644
--- a/chrome/browser/sync/test/integration/sync_extension_helper.cc
+++ b/chrome/browser/sync/test/integration/sync_extension_helper.cc
@@ -78,22 +78,22 @@ std::vector<std::string> SyncExtensionHelper::GetInstalledExtensionNames(
   std::vector<std::string> names;
   ExtensionService* extension_service = profile->GetExtensionService();
 
-  const ExtensionList* extensions = extension_service->extensions();
-  for (ExtensionList::const_iterator it = extensions->begin();
+  const ExtensionSet* extensions = extension_service->extensions();
+  for (ExtensionSet::const_iterator it = extensions->begin();
        it != extensions->end(); ++it) {
     names.push_back((*it)->name());
   }
 
-  const ExtensionList* disabled_extensions =
+  const ExtensionSet* disabled_extensions =
       extension_service->disabled_extensions();
-  for (ExtensionList::const_iterator it = disabled_extensions->begin();
+  for (ExtensionSet::const_iterator it = disabled_extensions->begin();
        it != disabled_extensions->end(); ++it) {
     names.push_back((*it)->name());
   }
 
-  const ExtensionList* terminated_extensions =
+  const ExtensionSet* terminated_extensions =
       extension_service->terminated_extensions();
-  for (ExtensionList::const_iterator it = terminated_extensions->begin();
+  for (ExtensionSet::const_iterator it = terminated_extensions->begin();
        it != terminated_extensions->end(); ++it) {
     names.push_back((*it)->name());
   }
@@ -180,8 +180,8 @@ SyncExtensionHelper::ExtensionStateMap
 
   ExtensionService* extension_service = profile->GetExtensionService();
 
-  const ExtensionList* extensions = extension_service->extensions();
-  for (ExtensionList::const_iterator it = extensions->begin();
+  const ExtensionSet* extensions = extension_service->extensions();
+  for (ExtensionSet::const_iterator it = extensions->begin();
        it != extensions->end(); ++it) {
     const std::string& id = (*it)->id();
     extension_state_map[id].enabled_state = ExtensionState::ENABLED;
@@ -191,9 +191,9 @@ SyncExtensionHelper::ExtensionStateMap
              << profile_debug_name << " is enabled";
   }
 
-  const ExtensionList* disabled_extensions =
+  const ExtensionSet* disabled_extensions =
       extension_service->disabled_extensions();
-  for (ExtensionList::const_iterator it = disabled_extensions->begin();
+  for (ExtensionSet::const_iterator it = disabled_extensions->begin();
        it != disabled_extensions->end(); ++it) {
     const std::string& id = (*it)->id();
     extension_state_map[id].enabled_state = ExtensionState::DISABLED;
diff --git a/chrome/browser/themes/theme_service.cc b/chrome/browser/themes/theme_service.cc
index 210e663..c4a62916 100644
--- a/chrome/browser/themes/theme_service.cc
+++ b/chrome/browser/themes/theme_service.cc
@@ -338,8 +338,8 @@ void ThemeService::RemoveUnusedThemes() {
     return;
   std::string current_theme = GetThemeID();
   std::vector<std::string> remove_list;
-  const ExtensionList* extensions = service->extensions();
-  for (ExtensionList::const_iterator it = extensions->begin();
+  const ExtensionSet* extensions = service->extensions();
+  for (ExtensionSet::const_iterator it = extensions->begin();
        it != extensions->end(); ++it) {
     if ((*it)->is_theme() && (*it)->id() != current_theme) {
       remove_list.push_back((*it)->id());
diff --git a/chrome/browser/ui/browser_browsertest.cc b/chrome/browser/ui/browser_browsertest.cc
index 173945f..d35cecb 100644
--- a/chrome/browser/ui/browser_browsertest.cc
+++ b/chrome/browser/ui/browser_browsertest.cc
@@ -164,11 +164,12 @@ class BrowserTest : public ExtensionBrowserTest {
 
   // Returns the app extension aptly named "App Test".
   const Extension* GetExtension() {
-    const ExtensionList* extensions =
+    const ExtensionSet* extensions =
         browser()->profile()->GetExtensionService()->extensions();
-    for (size_t i = 0; i < extensions->size(); ++i) {
-      if ((*extensions)[i]->name() == "App Test")
-        return (*extensions)[i];
+    for (ExtensionSet::const_iterator it = extensions->begin();
+         it != extensions->end(); ++it) {
+      if ((*it)->name() == "App Test")
+        return *it;
     }
     NOTREACHED();
     return NULL;
diff --git a/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm b/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
index 400078e..b251cd3 100644
--- a/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
+++ b/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
@@ -540,10 +540,12 @@ void LocationBarViewMac::RefreshPageActionDecorations() {
   if (!service)
     return;
 
+  // Find all the page actions.
   std::vector<ExtensionAction*> page_actions;
-  for (size_t i = 0; i < service->extensions()->size(); ++i) {
-    if (service->extensions()->at(i)->page_action())
-      page_actions.push_back(service->extensions()->at(i)->page_action());
+  for (ExtensionSet::const_iterator it = service->extensions()->begin();
+       it != service->extensions()->end(); ++it) {
+    if ((*it)->page_action())
+      page_actions.push_back((*it)->page_action());
   }
 
   // On startup we sometimes haven't loaded any extensions. This makes sure
diff --git a/chrome/browser/ui/gtk/location_bar_view_gtk.cc b/chrome/browser/ui/gtk/location_bar_view_gtk.cc
index 30a04f9..83407de 100644
--- a/chrome/browser/ui/gtk/location_bar_view_gtk.cc
+++ b/chrome/browser/ui/gtk/location_bar_view_gtk.cc
@@ -642,9 +642,10 @@ void LocationBarViewGtk::UpdatePageActions() {
     return;
 
   // Find all the page actions.
-  for (size_t i = 0; i < service->extensions()->size(); ++i) {
-    if (service->extensions()->at(i)->page_action())
-      page_actions.push_back(service->extensions()->at(i)->page_action());
+  for (ExtensionSet::const_iterator it = service->extensions()->begin();
+       it != service->extensions()->end(); ++it) {
+    if ((*it)->page_action())
+      page_actions.push_back((*it)->page_action());
   }
 
   // Initialize on the first call, or re-inialize if more extensions have been
diff --git a/chrome/browser/ui/views/browser_actions_container_browsertest.cc b/chrome/browser/ui/views/browser_actions_container_browsertest.cc
index 08b6133..0b7b04a 100644
--- a/chrome/browser/ui/views/browser_actions_container_browsertest.cc
+++ b/chrome/browser/ui/views/browser_actions_container_browsertest.cc
@@ -242,17 +242,14 @@ IN_PROC_BROWSER_TEST_F(BrowserActionsContainerTest, ForceHide) {
 IN_PROC_BROWSER_TEST_F(BrowserActionsContainerTest, TestCrash57536) {
   LOG(INFO) << "Test starting\n" << std::flush;
 
-  ExtensionService* service = browser()->profile()->GetExtensionService();
-  const size_t size_before = service->extensions()->size();
-
   LOG(INFO) << "Loading extension\n" << std::flush;
 
   // Load extension A (contains browser action).
-  ASSERT_TRUE(LoadExtension(test_data_dir_.AppendASCII("api_test")
-                                          .AppendASCII("browser_action")
-                                          .AppendASCII("crash_57536")));
-
-  const Extension* extension = service->extensions()->at(size_before);
+  const Extension* extension = LoadExtension(
+      test_data_dir_.AppendASCII("api_test")
+      .AppendASCII("browser_action")
+      .AppendASCII("crash_57536"));
+  ASSERT_TRUE(extension);
 
   LOG(INFO) << "Creating bitmap\n" << std::flush;
 
diff --git a/chrome/browser/ui/views/location_bar/location_bar_view.cc b/chrome/browser/ui/views/location_bar/location_bar_view.cc
index 848cc5c..f05ee66 100644
--- a/chrome/browser/ui/views/location_bar/location_bar_view.cc
+++ b/chrome/browser/ui/views/location_bar/location_bar_view.cc
@@ -925,9 +925,10 @@ void LocationBarView::RefreshPageActionViews() {
   // Remember the previous visibility of the page actions so that we can
   // notify when this changes.
   std::vector<ExtensionAction*> page_actions;
-  for (size_t i = 0; i < service->extensions()->size(); ++i) {
-    if (service->extensions()->at(i)->page_action())
-      page_actions.push_back(service->extensions()->at(i)->page_action());
+  for (ExtensionSet::const_iterator it = service->extensions()->begin();
+       it != service->extensions()->end(); ++it) {
+    if ((*it)->page_action())
+      page_actions.push_back((*it)->page_action());
   }
 
   // On startup we sometimes haven't loaded any extensions. This makes sure
diff --git a/chrome/browser/ui/webui/ntp/app_launcher_handler.cc b/chrome/browser/ui/webui/ntp/app_launcher_handler.cc
index 02752d8..424bc0e 100644
--- a/chrome/browser/ui/webui/ntp/app_launcher_handler.cc
+++ b/chrome/browser/ui/webui/ntp/app_launcher_handler.cc
@@ -331,11 +331,12 @@ void AppLauncherHandler::FillAppDictionary(DictionaryValue* dictionary) {
   AutoReset<bool> auto_reset(&ignore_changes_, true);
 
   ListValue* list = new ListValue();
-  const ExtensionList* extensions = extension_service_->extensions();
-  ExtensionList::const_iterator it;
+  const ExtensionSet* extensions = extension_service_->extensions();
+  ExtensionSet::const_iterator it;
   for (it = extensions->begin(); it != extensions->end(); ++it) {
-    if (!IsAppExcludedFromList(*it)) {
-      DictionaryValue* app_info = GetAppInfo(*it);
+    const Extension* extension = *it;
+    if (!IsAppExcludedFromList(extension)) {
+      DictionaryValue* app_info = GetAppInfo(extension);
       list->Append(app_info);
     } else {
       // This is necessary because in some previous versions of chrome, we set a
@@ -343,8 +344,8 @@ void AppLauncherHandler::FillAppDictionary(DictionaryValue* dictionary) {
       // and this fixes it. If we don't fix it, GetNaturalAppPageIndex() doesn't
       // work. See http://crbug.com/98325
       ExtensionPrefs* prefs = extension_service_->extension_prefs();
-      if (prefs->GetPageIndex((*it)->id()) != -1)
-        prefs->ClearPageIndex((*it)->id());
+      if (prefs->GetPageIndex(extension->id()) != -1)
+        prefs->ClearPageIndex(extension->id());
     }
   }
 
diff --git a/chrome/browser/ui/webui/options/extension_settings_handler.cc b/chrome/browser/ui/webui/options/extension_settings_handler.cc
index 6dff20f..222f713 100644
--- a/chrome/browser/ui/webui/options/extension_settings_handler.cc
+++ b/chrome/browser/ui/webui/options/extension_settings_handler.cc
@@ -150,8 +150,8 @@ void ExtensionSettingsHandler::HandleRequestExtensionsData(
 
   ExtensionWarningSet* warnings = extension_service_->extension_warnings();
 
-  const ExtensionList* extensions = extension_service_->extensions();
-  for (ExtensionList::const_iterator extension = extensions->begin();
+  const ExtensionSet* extensions = extension_service_->extensions();
+  for (ExtensionSet::const_iterator extension = extensions->begin();
        extension != extensions->end(); ++extension) {
     if (ShouldShowExtension(*extension)) {
       extensions_list->Append(CreateExtensionDetailValue(
@@ -163,7 +163,7 @@ void ExtensionSettingsHandler::HandleRequestExtensionsData(
     }
   }
   extensions = extension_service_->disabled_extensions();
-  for (ExtensionList::const_iterator extension = extensions->begin();
+  for (ExtensionSet::const_iterator extension = extensions->begin();
        extension != extensions->end(); ++extension) {
     if (ShouldShowExtension(*extension)) {
       extensions_list->Append(CreateExtensionDetailValue(
@@ -176,7 +176,7 @@ void ExtensionSettingsHandler::HandleRequestExtensionsData(
   }
   extensions = extension_service_->terminated_extensions();
   std::vector<ExtensionPage> empty_pages;
-  for (ExtensionList::const_iterator extension = extensions->begin();
+  for (ExtensionSet::const_iterator extension = extensions->begin();
        extension != extensions->end(); ++extension) {
     if (ShouldShowExtension(*extension)) {
       extensions_list->Append(CreateExtensionDetailValue(
diff --git a/chrome/browser/ui/webui/options/search_engine_manager_handler.cc b/chrome/browser/ui/webui/options/search_engine_manager_handler.cc
index e73b26a..1748e3a 100644
--- a/chrome/browser/ui/webui/options/search_engine_manager_handler.cc
+++ b/chrome/browser/ui/webui/options/search_engine_manager_handler.cc
@@ -143,8 +143,8 @@ void SearchEngineManagerHandler::OnModelChanged() {
   ExtensionService* extension_service =
       Profile::FromWebUI(web_ui_)->GetExtensionService();
   if (extension_service) {
-    const ExtensionList* extensions = extension_service->extensions();
-    for (ExtensionList::const_iterator it = extensions->begin();
+    const ExtensionSet* extensions = extension_service->extensions();
+    for (ExtensionSet::const_iterator it = extensions->begin();
          it != extensions->end(); ++it) {
       if ((*it)->omnibox_keyword().size() > 0)
         keyword_list.Append(CreateDictionaryForExtension(*(*it)));
diff --git a/chrome/common/extensions/extension_set.cc b/chrome/common/extensions/extension_set.cc
index 0231115..c99220b 100644
--- a/chrome/common/extensions/extension_set.cc
+++ b/chrome/common/extensions/extension_set.cc
@@ -29,6 +29,10 @@ size_t ExtensionSet::size() const {
   return extensions_.size();
 }
 
+bool ExtensionSet::is_empty() const {
+  return extensions_.empty();
+}
+
 bool ExtensionSet::Contains(const std::string& extension_id) const {
   return extensions_.find(extension_id) != extensions_.end();
 }
@@ -41,7 +45,11 @@ void ExtensionSet::Remove(const std::string& id) {
   extensions_.erase(id);
 }
 
-std::string ExtensionSet::GetIdByURL(const ExtensionURLInfo& info) const {
+void ExtensionSet::Clear() {
+  extensions_.clear();
+}
+
+std::string ExtensionSet::GetIDByURL(const ExtensionURLInfo& info) const {
   DCHECK(!info.origin().isNull());
 
   if (info.url().SchemeIs(chrome::kExtensionScheme))
diff --git a/chrome/common/extensions/extension_set.h b/chrome/common/extensions/extension_set.h
index 5ca0344..3407557 100644
--- a/chrome/common/extensions/extension_set.h
+++ b/chrome/common/extensions/extension_set.h
@@ -6,9 +6,9 @@
 #define CHROME_COMMON_EXTENSIONS_EXTENSION_SET_H_
 #pragma once
 
+#include <iterator>
 #include <map>
 #include <string>
-#include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/memory/ref_counted.h"
@@ -44,17 +44,39 @@ class ExtensionSet {
  public:
   typedef std::pair<FilePath, std::string> ExtensionPathAndDefaultLocale;
   typedef std::map<std::string, scoped_refptr<const Extension> > ExtensionMap;
-  typedef ExtensionMap::const_iterator const_iterator;
+
+  // Iteration over the values of the map (given that it's an ExtensionSet,
+  // it should iterate like a set iterator).
+  class const_iterator :
+      public std::iterator<std::input_iterator_tag,
+                           scoped_refptr<const Extension> > {
+   public:
+    const_iterator() {}
+    explicit const_iterator(ExtensionMap::const_iterator it) :
+        it_(it) {}
+    const_iterator& operator++() {
+      ++it_;
+      return *this;
+    }
+    const scoped_refptr<const Extension> operator*() {
+      return it_->second;
+    }
+    bool operator!=(const const_iterator& other) { return it_ != other.it_; }
+    bool operator==(const const_iterator& other) { return it_ == other.it_; }
+
+   private:
+    ExtensionMap::const_iterator it_;
+  };
 
   ExtensionSet();
   ~ExtensionSet();
 
-  // Gets the number of extensions contained.
   size_t size() const;
+  bool is_empty() const;
 
   // Iteration support.
-  const_iterator begin() const { return extensions_.begin(); }
-  const_iterator end() const { return extensions_.end(); }
+  const_iterator begin() const { return const_iterator(extensions_.begin()); }
+  const_iterator end() const { return const_iterator(extensions_.end()); }
 
   // Returns true if the set contains the specified extension.
   bool Contains(const std::string& id) const;
@@ -66,9 +88,12 @@ class ExtensionSet {
   // Removes the specified extension.
   void Remove(const std::string& id);
 
+  // Removes all extensions.
+  void Clear();
+
   // Returns the extension ID, or empty if none. This includes web URLs that
   // are part of an extension's web extent.
-  std::string GetIdByURL(const ExtensionURLInfo& info) const;
+  std::string GetIDByURL(const ExtensionURLInfo& info) const;
 
   // Returns the Extension, or NULL if none.  This includes web URLs that are
   // part of an extension's web extent.
diff --git a/chrome/renderer/extensions/extension_dispatcher.cc b/chrome/renderer/extensions/extension_dispatcher.cc
index cc003fd..c33b488 100644
--- a/chrome/renderer/extensions/extension_dispatcher.cc
+++ b/chrome/renderer/extensions/extension_dispatcher.cc
@@ -293,7 +293,7 @@ void ExtensionDispatcher::DidCreateScriptContext(
     extension_id = user_script_slave_->GetExtensionIdForIsolatedWorld(world_id);
   } else {
     GURL frame_url = UserScriptSlave::GetDataSourceURLForFrame(frame);
-    extension_id = extensions_.GetIdByURL(
+    extension_id = extensions_.GetIDByURL(
       ExtensionURLInfo(frame->document().securityOrigin(), frame_url));
   }