content: convert zoom notifications to callbacks

BUG=170921

Review URL: https://codereview.chromium.org/12039058

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@181307 0039d316-1c4b-4281-b951-d872f2087c98

21 files changed, 284 insertions, 213 deletions

diff --git a/chrome/browser/profiles/off_the_record_profile_impl.cc b/chrome/browser/profiles/off_the_record_profile_impl.cc
index ce72d61..87f30a2 100644
--- a/chrome/browser/profiles/off_the_record_profile_impl.cc
+++ b/chrome/browser/profiles/off_the_record_profile_impl.cc
@@ -44,8 +44,6 @@
 #include "chrome/common/render_messages.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/host_zoom_map.h"
-#include "content/public/browser/notification_service.h"
-#include "content/public/browser/notification_types.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/storage_partition.h"
 #include "content/public/browser/url_data_source.h"
@@ -87,7 +85,9 @@ OffTheRecordProfileImpl::OffTheRecordProfileImpl(Profile* real_profile)
     : profile_(real_profile),
       prefs_(real_profile->GetOffTheRecordPrefs()),
       ALLOW_THIS_IN_INITIALIZER_LIST(io_data_(this)),
-      start_time_(Time::Now()) {
+      start_time_(Time::Now()),
+      zoom_callback_(base::Bind(&OffTheRecordProfileImpl::OnZoomLevelChanged,
+                                base::Unretained(this))) {
 }
 
 void OffTheRecordProfileImpl::Init() {
@@ -129,6 +129,9 @@ void OffTheRecordProfileImpl::Init() {
 OffTheRecordProfileImpl::~OffTheRecordProfileImpl() {
   MaybeSendDestroyedNotification();
 
+  HostZoomMap::GetForBrowserContext(profile_)->RemoveZoomLevelChangedCallback(
+      zoom_callback_);
+
 #if defined(ENABLE_PLUGINS)
   ChromePluginServiceFilter::GetInstance()->UnregisterResourceContext(
     io_data_.GetResourceContextNoInit());
@@ -165,8 +168,7 @@ void OffTheRecordProfileImpl::InitHostZoomMap() {
   host_zoom_map->CopyFrom(parent_host_zoom_map);
   // Observe parent's HZM change for propagating change of parent's
   // change to this HZM.
-  registrar_.Add(this, content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-                 content::Source<HostZoomMap>(parent_host_zoom_map));
+  parent_host_zoom_map->AddZoomLevelChangedCallback(zoom_callback_);
 }
 
 #if defined(OS_ANDROID)
@@ -428,23 +430,6 @@ GURL OffTheRecordProfileImpl::GetHomePage() {
   return profile_->GetHomePage();
 }
 
-void OffTheRecordProfileImpl::Observe(
-    int type,
-    const content::NotificationSource& source,
-    const content::NotificationDetails& details) {
-  if (type == content::NOTIFICATION_ZOOM_LEVEL_CHANGED) {
-    const std::string& host =
-        *(content::Details<const std::string>(details).ptr());
-    if (!host.empty()) {
-      HostZoomMap* host_zoom_map = HostZoomMap::GetForBrowserContext(this);
-      HostZoomMap* parent_host_zoom_map =
-          HostZoomMap::GetForBrowserContext(profile_);
-      double level = parent_host_zoom_map->GetZoomLevel(host);
-      host_zoom_map->SetZoomLevel(host, level);
-    }
-  }
-}
-
 #if defined(OS_CHROMEOS)
 // Special case of the OffTheRecordProfileImpl which is used while Guest
 // session in CrOS.
@@ -476,3 +461,14 @@ Profile* Profile::CreateOffTheRecordProfile() {
   profile->Init();
   return profile;
 }
+
+void OffTheRecordProfileImpl::OnZoomLevelChanged(const std::string& host) {
+  if (host.empty())
+    return;
+
+  HostZoomMap* host_zoom_map = HostZoomMap::GetForBrowserContext(this);
+  HostZoomMap* parent_host_zoom_map =
+      HostZoomMap::GetForBrowserContext(profile_);
+  double level = parent_host_zoom_map->GetZoomLevel(host);
+  host_zoom_map->SetZoomLevel(host, level);
+}
diff --git a/chrome/browser/profiles/off_the_record_profile_impl.h b/chrome/browser/profiles/off_the_record_profile_impl.h
index 3066eae..8b659bd 100644
--- a/chrome/browser/profiles/off_the_record_profile_impl.h
+++ b/chrome/browser/profiles/off_the_record_profile_impl.h
@@ -11,8 +11,7 @@
 #include "chrome/browser/profiles/off_the_record_profile_io_data.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser_list.h"
-#include "content/public/browser/notification_observer.h"
-#include "content/public/browser/notification_registrar.h"
+#include "content/public/browser/host_zoom_map.h"
 
 using base::Time;
 using base::TimeDelta;
@@ -26,8 +25,7 @@ using base::TimeDelta;
 // Providing this header file is for unit testing.
 //
 ////////////////////////////////////////////////////////////////////////////////
-class OffTheRecordProfileImpl : public Profile,
-                                public content::NotificationObserver {
+class OffTheRecordProfileImpl : public Profile {
  public:
   explicit OffTheRecordProfileImpl(Profile* real_profile);
   virtual ~OffTheRecordProfileImpl();
@@ -105,11 +103,6 @@ class OffTheRecordProfileImpl : public Profile,
       GetSpeechRecognitionPreferences() OVERRIDE;
   virtual quota::SpecialStoragePolicy* GetSpecialStoragePolicy() OVERRIDE;
 
-  // content::NotificationObserver implementation.
-  virtual void Observe(int type,
-                       const content::NotificationSource& source,
-                       const content::NotificationDetails& details) OVERRIDE;
-
  private:
   FRIEND_TEST_ALL_PREFIXES(OffTheRecordProfileImplTest, GetHostZoomMap);
   void InitHostZoomMap();
@@ -118,7 +111,7 @@ class OffTheRecordProfileImpl : public Profile,
   void UseSystemProxy();
 #endif
 
-  content::NotificationRegistrar registrar_;
+  void OnZoomLevelChanged(const std::string& host);
 
   // The real underlying profile.
   Profile* profile_;
@@ -138,6 +131,8 @@ class OffTheRecordProfileImpl : public Profile,
 
   scoped_ptr<PrefProxyConfigTracker> pref_proxy_config_tracker_;
 
+  content::HostZoomMap::ZoomLevelChangedCallback zoom_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(OffTheRecordProfileImpl);
 };
 
diff --git a/chrome/browser/profiles/off_the_record_profile_impl_unittest.cc b/chrome/browser/profiles/off_the_record_profile_impl_unittest.cc
index b8572c5..4bd5c2b 100644
--- a/chrome/browser/profiles/off_the_record_profile_impl_unittest.cc
+++ b/chrome/browser/profiles/off_the_record_profile_impl_unittest.cc
@@ -16,24 +16,25 @@
 #include "chrome/test/base/testing_pref_service.h"
 #include "chrome/test/base/testing_profile.h"
 #include "content/public/browser/host_zoom_map.h"
-#include "content/public/browser/notification_details.h"
-#include "content/public/browser/notification_source.h"
-#include "content/public/browser/notification_types.h"
 
 using content::HostZoomMap;
 
 namespace {
 
-class TestingProfileWithHostZoomMap : public TestingProfile,
-                                      public content::NotificationObserver {
+class TestingProfileWithHostZoomMap : public TestingProfile {
  public:
-  TestingProfileWithHostZoomMap() {
-    HostZoomMap* host_zoom_map = HostZoomMap::GetForBrowserContext(this);
-    registrar_.Add(this, content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-                   content::Source<HostZoomMap>(host_zoom_map));
+  TestingProfileWithHostZoomMap()
+      : zoom_callback_(
+          base::Bind(&TestingProfileWithHostZoomMap::OnZoomLevelChanged,
+                     base::Unretained(this))) {
+    HostZoomMap::GetForBrowserContext(this)->AddZoomLevelChangedCallback(
+        zoom_callback_);
   }
 
-  virtual ~TestingProfileWithHostZoomMap() {}
+  virtual ~TestingProfileWithHostZoomMap() {
+    HostZoomMap::GetForBrowserContext(this)->RemoveZoomLevelChangedCallback(
+        zoom_callback_);
+  }
 
   virtual Profile* GetOffTheRecordProfile() OVERRIDE {
     if (!off_the_record_profile_.get())
@@ -45,12 +46,8 @@ class TestingProfileWithHostZoomMap : public TestingProfile,
     return GetPrefs();
   }
 
-  virtual void Observe(int type,
-                       const content::NotificationSource& source,
-                       const content::NotificationDetails& details) OVERRIDE {
-    const std::string& host =
-        *(content::Details<const std::string>(details).ptr());
-    DCHECK(type == content::NOTIFICATION_ZOOM_LEVEL_CHANGED);
+ private:
+  void OnZoomLevelChanged(const std::string& host) {
     if (host.empty())
       return;
 
@@ -66,11 +63,11 @@ class TestingProfileWithHostZoomMap : public TestingProfile,
     }
   }
 
- private:
-  content::NotificationRegistrar registrar_;
   scoped_ptr<Profile> off_the_record_profile_;
   scoped_ptr<SSLConfigServiceManager> ssl_config_service_manager_;
 
+  content::HostZoomMap::ZoomLevelChangedCallback zoom_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(TestingProfileWithHostZoomMap);
 };
 
@@ -138,7 +135,7 @@ TEST_F(OffTheRecordProfileImplTest, GetHostZoomMap) {
   ASSERT_EQ(parent_zoom_map->GetZoomLevel(host), zoom_level_25);
 
   // TODO(yosin) We need to wait ProfileImpl::Observe done for
-  // NOTIFICATION_ZOOM_LEVEL_CHANGED.
+  // OnZoomLevelChanged.
 
   // Prepare child profile as off the record profile.
   scoped_ptr<OffTheRecordProfileImpl> child_profile(
diff --git a/chrome/browser/profiles/profile_impl.cc b/chrome/browser/profiles/profile_impl.cc
index ddb9b5a..06716b8 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -322,7 +322,9 @@ ProfileImpl::ProfileImpl(
     Delegate* delegate,
     CreateMode create_mode,
     base::SequencedTaskRunner* sequenced_task_runner)
-    : path_(path),
+    : zoom_callback_(base::Bind(&ProfileImpl::OnZoomLevelChanged,
+                                base::Unretained(this))),
+      path_(path),
       ALLOW_THIS_IN_INITIALIZER_LIST(io_data_(this)),
       host_content_settings_map_(NULL),
       last_session_exit_type_(EXIT_NORMAL),
@@ -567,8 +569,7 @@ void ProfileImpl::InitHostZoomMap() {
     }
   }
 
-  registrar_.Add(this, content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-                 content::Source<HostZoomMap>(host_zoom_map));
+  host_zoom_map->AddZoomLevelChangedCallback(zoom_callback_);
 }
 
 FilePath ProfileImpl::last_selected_directory() {
@@ -582,6 +583,9 @@ void ProfileImpl::set_last_selected_directory(const FilePath& path) {
 ProfileImpl::~ProfileImpl() {
   MaybeSendDestroyedNotification();
 
+  HostZoomMap::GetForBrowserContext(this)->RemoveZoomLevelChangedCallback(
+      zoom_callback_);
+
   bool prefs_loaded = prefs_->GetInitializationStatus() !=
       PrefService::INITIALIZATION_STATUS_WAITING;
 
@@ -930,23 +934,6 @@ void ProfileImpl::Observe(int type,
       registrar_.Remove(this, chrome::NOTIFICATION_BOOKMARK_MODEL_LOADED,
                         content::Source<Profile>(this));
       break;
-    case content::NOTIFICATION_ZOOM_LEVEL_CHANGED: {
-      const std::string& host =
-          *(content::Details<const std::string>(details).ptr());
-      if (!host.empty()) {
-        HostZoomMap* host_zoom_map = HostZoomMap::GetForBrowserContext(this);
-        double level = host_zoom_map->GetZoomLevel(host);
-        DictionaryPrefUpdate update(prefs_.get(), prefs::kPerHostZoomLevels);
-        DictionaryValue* host_zoom_dictionary = update.Get();
-        if (level == host_zoom_map->GetDefaultZoomLevel()) {
-          host_zoom_dictionary->RemoveWithoutPathExpansion(host, NULL);
-        } else {
-          host_zoom_dictionary->SetWithoutPathExpansion(
-              host, Value::CreateDoubleValue(level));
-        }
-      }
-      break;
-    }
     default:
       NOTREACHED();
   }
@@ -957,6 +944,21 @@ void ProfileImpl::OnDefaultZoomLevelChanged() {
       pref_change_registrar_.prefs()->GetDouble(prefs::kDefaultZoomLevel));
 }
 
+void ProfileImpl::OnZoomLevelChanged(const std::string& host) {
+  if (host.empty())
+    return;
+  HostZoomMap* host_zoom_map = HostZoomMap::GetForBrowserContext(this);
+  double level = host_zoom_map->GetZoomLevel(host);
+  DictionaryPrefUpdate update(prefs_.get(), prefs::kPerHostZoomLevels);
+  DictionaryValue* host_zoom_dictionary = update.Get();
+  if (level == host_zoom_map->GetDefaultZoomLevel()) {
+    host_zoom_dictionary->RemoveWithoutPathExpansion(host, NULL);
+  } else {
+    host_zoom_dictionary->SetWithoutPathExpansion(
+        host, Value::CreateDoubleValue(level));
+  }
+}
+
 #if defined(ENABLE_SESSION_SERVICE)
 void ProfileImpl::StopCreateSessionServiceTimer() {
   create_session_service_timer_.Stop();
diff --git a/chrome/browser/profiles/profile_impl.h b/chrome/browser/profiles/profile_impl.h
index 87d2c1d..2c81c8c 100644
--- a/chrome/browser/profiles/profile_impl.h
+++ b/chrome/browser/profiles/profile_impl.h
@@ -19,6 +19,7 @@
 #include "chrome/browser/profiles/profile_impl_io_data.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
+#include "content/public/browser/host_zoom_map.h"
 
 class NetPrefObserver;
 class PrefServiceSyncable;
@@ -159,6 +160,7 @@ class ProfileImpl : public Profile,
   void InitHostZoomMap();
 
   void OnDefaultZoomLevelChanged();
+  void OnZoomLevelChanged(const std::string& host);
 
   void OnInitializationCompleted(PrefServiceBase* pref_service,
                                  bool succeeded);
@@ -190,6 +192,7 @@ class ProfileImpl : public Profile,
                           int* max_size);
 
   content::NotificationRegistrar registrar_;
+  content::HostZoomMap::ZoomLevelChangedCallback zoom_callback_;
   PrefChangeRegistrar pref_change_registrar_;
 
   FilePath path_;
diff --git a/chrome/browser/ui/browser_browsertest.cc b/chrome/browser/ui/browser_browsertest.cc
index 26275a5..5ec5439 100644
--- a/chrome/browser/ui/browser_browsertest.cc
+++ b/chrome/browser/ui/browser_browsertest.cc
@@ -49,11 +49,10 @@
 #include "chrome/test/base/in_process_browser_test.h"
 #include "chrome/test/base/ui_test_utils.h"
 #include "content/public/browser/favicon_status.h"
+#include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/interstitial_page.h"
 #include "content/public/browser/interstitial_page_delegate.h"
 #include "content/public/browser/navigation_entry.h"
-#include "content/public/browser/notification_service.h"
-#include "content/public/browser/notification_source.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/render_widget_host_view.h"
@@ -1322,6 +1321,15 @@ IN_PROC_BROWSER_TEST_F(BrowserTest,
   EXPECT_FALSE(command_updater->IsCommandEnabled(IDC_IMPORT_SETTINGS));
 }
 
+namespace {
+
+void OnZoomLevelChanged(const base::Closure& callback,
+                        const std::string& host) {
+  callback.Run();
+}
+
+}  // namespace
+
 #if defined(OS_WIN)
 // Flakes regularly on Windows XP
 // http://crbug.com/146040
@@ -1333,32 +1341,53 @@ IN_PROC_BROWSER_TEST_F(BrowserTest, MAYBE_PageZoom) {
   WebContents* contents = browser()->tab_strip_model()->GetActiveWebContents();
   bool enable_plus, enable_minus;
 
-  content::WindowedNotificationObserver zoom_in_observer(
-      content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-      content::NotificationService::AllSources());
-  chrome::Zoom(browser(), content::PAGE_ZOOM_IN);
-  zoom_in_observer.Wait();
-  EXPECT_EQ(contents->GetZoomPercent(&enable_plus, &enable_minus), 110);
-  EXPECT_TRUE(enable_plus);
-  EXPECT_TRUE(enable_minus);
-
-  content::WindowedNotificationObserver zoom_reset_observer(
-      content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-      content::NotificationService::AllSources());
-  chrome::Zoom(browser(), content::PAGE_ZOOM_RESET);
-  zoom_reset_observer.Wait();
-  EXPECT_EQ(contents->GetZoomPercent(&enable_plus, &enable_minus), 100);
-  EXPECT_TRUE(enable_plus);
-  EXPECT_TRUE(enable_minus);
+  {
+    scoped_refptr<content::MessageLoopRunner> loop_runner(
+        new content::MessageLoopRunner);
+    content::HostZoomMap::ZoomLevelChangedCallback callback(
+        base::Bind(&OnZoomLevelChanged, loop_runner->QuitClosure()));
+    content::HostZoomMap::GetForBrowserContext(
+        browser()->profile())->AddZoomLevelChangedCallback(callback);
+    chrome::Zoom(browser(), content::PAGE_ZOOM_IN);
+    loop_runner->Run();
+    content::HostZoomMap::GetForBrowserContext(
+        browser()->profile())->RemoveZoomLevelChangedCallback(callback);
+    EXPECT_EQ(contents->GetZoomPercent(&enable_plus, &enable_minus), 110);
+    EXPECT_TRUE(enable_plus);
+    EXPECT_TRUE(enable_minus);
+  }
 
-  content::WindowedNotificationObserver zoom_out_observer(
-      content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-      content::NotificationService::AllSources());
-  chrome::Zoom(browser(), content::PAGE_ZOOM_OUT);
-  zoom_out_observer.Wait();
-  EXPECT_EQ(contents->GetZoomPercent(&enable_plus, &enable_minus), 90);
-  EXPECT_TRUE(enable_plus);
-  EXPECT_TRUE(enable_minus);
+  {
+    scoped_refptr<content::MessageLoopRunner> loop_runner(
+        new content::MessageLoopRunner);
+    content::HostZoomMap::ZoomLevelChangedCallback callback(
+        base::Bind(&OnZoomLevelChanged, loop_runner->QuitClosure()));
+    content::HostZoomMap::GetForBrowserContext(
+        browser()->profile())->AddZoomLevelChangedCallback(callback);
+    chrome::Zoom(browser(), content::PAGE_ZOOM_RESET);
+    loop_runner->Run();
+    content::HostZoomMap::GetForBrowserContext(
+        browser()->profile())->RemoveZoomLevelChangedCallback(callback);
+    EXPECT_EQ(contents->GetZoomPercent(&enable_plus, &enable_minus), 100);
+    EXPECT_TRUE(enable_plus);
+    EXPECT_TRUE(enable_minus);
+  }
+
+  {
+    scoped_refptr<content::MessageLoopRunner> loop_runner(
+        new content::MessageLoopRunner);
+    content::HostZoomMap::ZoomLevelChangedCallback callback(
+        base::Bind(&OnZoomLevelChanged, loop_runner->QuitClosure()));
+    content::HostZoomMap::GetForBrowserContext(
+        browser()->profile())->AddZoomLevelChangedCallback(callback);
+    chrome::Zoom(browser(), content::PAGE_ZOOM_OUT);
+    loop_runner->Run();
+    content::HostZoomMap::GetForBrowserContext(
+        browser()->profile())->RemoveZoomLevelChangedCallback(callback);
+    EXPECT_EQ(contents->GetZoomPercent(&enable_plus, &enable_minus), 90);
+    EXPECT_TRUE(enable_plus);
+    EXPECT_TRUE(enable_minus);
+  }
 
   chrome::Zoom(browser(), content::PAGE_ZOOM_RESET);
 }
diff --git a/chrome/browser/ui/cocoa/wrench_menu/wrench_menu_controller.mm b/chrome/browser/ui/cocoa/wrench_menu/wrench_menu_controller.mm
index bb87814..8f1cc87 100644
--- a/chrome/browser/ui/cocoa/wrench_menu/wrench_menu_controller.mm
+++ b/chrome/browser/ui/cocoa/wrench_menu/wrench_menu_controller.mm
@@ -22,11 +22,6 @@
 #import "chrome/browser/ui/cocoa/wrench_menu/recent_tabs_menu_model_delegate.h"
 #include "chrome/browser/ui/toolbar/recent_tabs_sub_menu_model.h"
 #include "chrome/browser/ui/toolbar/wrench_menu_model.h"
-#include "content/public/browser/host_zoom_map.h"
-#include "content/public/browser/notification_observer.h"
-#include "content/public/browser/notification_service.h"
-#include "content/public/browser/notification_source.h"
-#include "content/public/browser/notification_types.h"
 #include "content/public/browser/user_metrics.h"
 #include "grit/chromium_strings.h"
 #include "grit/generated_resources.h"
@@ -64,35 +59,36 @@ class AcceleratorDelegate : public ui::AcceleratorProvider {
   }
 };
 
-class ZoomLevelObserver : public content::NotificationObserver {
+class ZoomLevelObserver {
  public:
-  explicit ZoomLevelObserver(WrenchMenuController* controller)
-      : controller_(controller) {
-    registrar_.Add(
-        this, content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-        content::NotificationService::AllBrowserContextsAndSources());
+  ZoomLevelObserver(WrenchMenuController* controller,
+                    content::HostZoomMap* map)
+      : callback_(base::Bind(&ZoomLevelObserver::OnZoomLevelChanged,
+                             base::Unretained(this))),
+        controller_(controller),
+        map_(map) {
+    map_->AddZoomLevelChangedCallback(callback_);
   }
 
-  void Observe(int type,
-               const content::NotificationSource& source,
-               const content::NotificationDetails& details) {
-    DCHECK_EQ(type, content::NOTIFICATION_ZOOM_LEVEL_CHANGED);
-    WrenchMenuModel* wrenchMenuModel = [controller_ wrenchMenuModel];
-    if (HostZoomMap::GetForBrowserContext(
-            wrenchMenuModel->browser()->profile()) !=
-        content::Source<HostZoomMap>(source).ptr()) {
-      return;
-    }
+  ~ZoomLevelObserver() {
+    map_->RemoveZoomLevelChangedCallback(callback_);
+  }
 
+ private:
+  void OnZoomLevelChanged(const std::string& host) {
+    WrenchMenuModel* wrenchMenuModel = [controller_ wrenchMenuModel];
     wrenchMenuModel->UpdateZoomControls();
     const string16 level =
         wrenchMenuModel->GetLabelForCommandId(IDC_ZOOM_PERCENT_DISPLAY);
     [[controller_ zoomDisplay] setTitle:SysUTF16ToNSString(level)];
   }
 
- private:
-  content::NotificationRegistrar registrar_;
+  content::HostZoomMap::ZoomLevelChangedCallback callback_;
+
   WrenchMenuController* controller_;  // Weak; owns this.
+  content::HostZoomMap* map_;  // Weak.
+
+  DISALLOW_COPY_AND_ASSIGN(ZoomLevelObserver);
 };
 
 }  // namespace WrenchMenuControllerInternal
@@ -102,7 +98,8 @@ class ZoomLevelObserver : public content::NotificationObserver {
 - (id)initWithBrowser:(Browser*)browser {
   if ((self = [super init])) {
     browser_ = browser;
-    observer_.reset(new WrenchMenuControllerInternal::ZoomLevelObserver(self));
+    observer_.reset(new WrenchMenuControllerInternal::ZoomLevelObserver(
+        self, content::HostZoomMap::GetForBrowserContext(browser->profile())));
     acceleratorDelegate_.reset(
         new WrenchMenuControllerInternal::AcceleratorDelegate());
     [self createModel];
diff --git a/chrome/browser/ui/cocoa/wrench_menu/wrench_menu_controller_unittest.mm b/chrome/browser/ui/cocoa/wrench_menu/wrench_menu_controller_unittest.mm
index f4f351b..a9aa99f 100644
--- a/chrome/browser/ui/cocoa/wrench_menu/wrench_menu_controller_unittest.mm
+++ b/chrome/browser/ui/cocoa/wrench_menu/wrench_menu_controller_unittest.mm
@@ -44,7 +44,7 @@ class MockWrenchMenuModel : public WrenchMenuModel {
 
 class WrenchMenuControllerTest : public CocoaProfileTest {
  public:
-  virtual void SetUp() {
+  virtual void SetUp() OVERRIDE {
     CocoaProfileTest::SetUp();
     ASSERT_TRUE(browser());
 
@@ -52,6 +52,12 @@ class WrenchMenuControllerTest : public CocoaProfileTest {
     fake_model_.reset(new MockWrenchMenuModel);
   }
 
+  virtual void TearDown() OVERRIDE {
+    fake_model_.reset();
+    controller_.reset();
+    CocoaProfileTest::TearDown();
+  }
+
   WrenchMenuController* controller() {
     return controller_.get();
   }
diff --git a/chrome/browser/ui/gtk/browser_toolbar_gtk.cc b/chrome/browser/ui/gtk/browser_toolbar_gtk.cc
index 11e1b2b..45b4581 100644
--- a/chrome/browser/ui/gtk/browser_toolbar_gtk.cc
+++ b/chrome/browser/ui/gtk/browser_toolbar_gtk.cc
@@ -99,7 +99,9 @@ BrowserToolbarGtk::BrowserToolbarGtk(Browser* browser, BrowserWindowGtk* window)
       model_(browser->toolbar_model()),
       is_wrench_menu_model_valid_(true),
       browser_(browser),
-      window_(window) {
+      window_(window),
+      zoom_callback_(base::Bind(&BrowserToolbarGtk::OnZoomLevelChanged,
+                                base::Unretained(this))) {
   wrench_menu_model_.reset(new WrenchMenuModel(this, browser_, false, false));
 
   chrome::AddCommandObserver(browser_, IDC_BACK, this);
@@ -124,6 +126,9 @@ BrowserToolbarGtk::~BrowserToolbarGtk() {
   offscreen_entry_.Destroy();
 
   wrench_menu_.reset();
+
+  HostZoomMap::GetForBrowserContext(
+      browser()->profile())->RemoveZoomLevelChangedCallback(zoom_callback_);
 }
 
 void BrowserToolbarGtk::Init(GtkWindow* top_level_window) {
@@ -241,9 +246,8 @@ void BrowserToolbarGtk::Init(GtkWindow* top_level_window) {
   // The bookmark menu model needs to be able to force the wrench menu to close.
   wrench_menu_model_->bookmark_sub_menu_model()->SetMenuGtk(wrench_menu_.get());
 
-  registrar_.Add(this, content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-      content::Source<HostZoomMap>(
-          HostZoomMap::GetForBrowserContext(profile)));
+  HostZoomMap::GetForBrowserContext(
+      browser()->profile())->AddZoomLevelChangedCallback(zoom_callback_);
 
   if (ShouldOnlyShowLocation()) {
     gtk_widget_show(event_box_);
@@ -416,18 +420,6 @@ void BrowserToolbarGtk::Observe(int type,
   } else if (type == chrome::NOTIFICATION_GLOBAL_ERRORS_CHANGED) {
     is_wrench_menu_model_valid_ = false;
     gtk_widget_queue_draw(wrench_menu_button_->widget());
-  } else if (type == content::NOTIFICATION_ZOOM_LEVEL_CHANGED) {
-    // Since BrowserToolbarGtk create a new |wrench_menu_model_| in
-    // RebuildWrenchMenu(), the ordering of the observers of
-    // NOTIFICATION_ZOOM_LEVEL_CHANGED can change, and result in subtle bugs
-    // like http://crbug.com/118823. Rather than depending on the ordering
-    // of the notification observers, always update the WrenchMenuModel before
-    // updating the WrenchMenu.
-    wrench_menu_model_->UpdateZoomControls();
-
-    // If our zoom level changed, we need to tell the menu to update its state,
-    // since the menu could still be open.
-    wrench_menu_->UpdateMenu();
   } else {
     NOTREACHED();
   }
@@ -449,6 +441,20 @@ bool BrowserToolbarGtk::IsWrenchMenuShowing() const {
 
 // BrowserToolbarGtk, private --------------------------------------------------
 
+void BrowserToolbarGtk::OnZoomLevelChanged(const std::string& host) {
+  // Since BrowserToolbarGtk create a new |wrench_menu_model_| in
+  // RebuildWrenchMenu(), the ordering of the observers of HostZoomMap
+  // can change, and result in subtle bugs like http://crbug.com/118823.
+  // Rather than depending on the ordering of the observers, always update
+  // the WrenchMenuModel before updating the WrenchMenu.
+  wrench_menu_model_->UpdateZoomControls();
+
+  // If our zoom level changed, we need to tell the menu to update its state,
+  // since the menu could still be open.
+  wrench_menu_->UpdateMenu();
+}
+
+
 void BrowserToolbarGtk::SetUpDragForHomeButton() {
   if (!home_page_.IsManaged() && !home_page_is_new_tab_page_.IsManaged()) {
     gtk_drag_dest_set(home_->widget(), GTK_DEST_DEFAULT_ALL,
diff --git a/chrome/browser/ui/gtk/browser_toolbar_gtk.h b/chrome/browser/ui/gtk/browser_toolbar_gtk.h
index 932d142..e988156 100644
--- a/chrome/browser/ui/gtk/browser_toolbar_gtk.h
+++ b/chrome/browser/ui/gtk/browser_toolbar_gtk.h
@@ -15,6 +15,7 @@
 #include "chrome/browser/ui/gtk/custom_button.h"
 #include "chrome/browser/ui/gtk/menu_gtk.h"
 #include "chrome/browser/ui/toolbar/wrench_menu_model.h"
+#include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "ui/base/accelerators/accelerator.h"
@@ -112,6 +113,8 @@ class BrowserToolbarGtk : public CommandObserver,
                          bool should_restore_state);
 
  private:
+  void OnZoomLevelChanged(const std::string& host);
+
   // Connect/Disconnect signals for dragging a url onto the home button.
   void SetUpDragForHomeButton();
 
@@ -211,6 +214,7 @@ class BrowserToolbarGtk : public CommandObserver,
   StringPrefMember home_page_;
   BooleanPrefMember home_page_is_new_tab_page_;
 
+  content::HostZoomMap::ZoomLevelChangedCallback zoom_callback_;
   content::NotificationRegistrar registrar_;
 
   // A GtkEntry that isn't part of the hierarchy. We keep this for native
diff --git a/chrome/browser/ui/gtk/location_bar_view_gtk_browsertest.cc b/chrome/browser/ui/gtk/location_bar_view_gtk_browsertest.cc
index 770f56e..5c53cf5 100644
--- a/chrome/browser/ui/gtk/location_bar_view_gtk_browsertest.cc
+++ b/chrome/browser/ui/gtk/location_bar_view_gtk_browsertest.cc
@@ -5,6 +5,7 @@
 #include <gtk/gtk.h>
 
 #include "base/string_number_conversions.h"
+#include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_commands.h"
 #include "chrome/browser/ui/browser_window.h"
@@ -16,6 +17,7 @@
 #include "chrome/browser/ui/zoom/zoom_controller.h"
 #include "chrome/test/base/in_process_browser_test.h"
 #include "chrome/test/base/ui_test_utils.h"
+#include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/web_contents.h"
@@ -44,8 +46,13 @@ void ExpectAtDefaultZoom(content::WebContents* contents) {
   EXPECT_EQ(GetZoomPercent(contents), 100);
 }
 
+void OnZoomLevelChanged(const base::Closure& callback,
+                        const std::string& host) {
+  callback.Run();
 }
 
+}  // namespace
+
 class LocationBarViewGtkZoomTest : public InProcessBrowserTest {
  public:
   LocationBarViewGtkZoomTest() {}
@@ -101,11 +108,16 @@ class LocationBarViewGtkZoomTest : public InProcessBrowserTest {
   }
 
   void WaitForZoom(content::PageZoom zoom_action) {
-    content::WindowedNotificationObserver zoom_observer(
-        content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-        content::NotificationService::AllSources());
+    scoped_refptr<content::MessageLoopRunner> loop_runner(
+        new content::MessageLoopRunner);
+    content::HostZoomMap::ZoomLevelChangedCallback callback(
+        base::Bind(&OnZoomLevelChanged, loop_runner->QuitClosure()));
+    content::HostZoomMap::GetForBrowserContext(
+        browser()->profile())->AddZoomLevelChangedCallback(callback);
     chrome::Zoom(browser(), zoom_action);
-    zoom_observer.Wait();
+    loop_runner->Run();
+    content::HostZoomMap::GetForBrowserContext(
+        browser()->profile())->RemoveZoomLevelChangedCallback(callback);
   }
 
   DISALLOW_COPY_AND_ASSIGN(LocationBarViewGtkZoomTest);
diff --git a/chrome/browser/ui/toolbar/wrench_menu_model.cc b/chrome/browser/ui/toolbar/wrench_menu_model.cc
index 6956729..c24ce72 100644
--- a/chrome/browser/ui/toolbar/wrench_menu_model.cc
+++ b/chrome/browser/ui/toolbar/wrench_menu_model.cc
@@ -212,16 +212,17 @@ WrenchMenuModel::WrenchMenuModel(ui::AcceleratorProvider* provider,
     : ALLOW_THIS_IN_INITIALIZER_LIST(ui::SimpleMenuModel(this)),
       provider_(provider),
       browser_(browser),
-      tab_strip_model_(browser_->tab_strip_model()) {
+      tab_strip_model_(browser_->tab_strip_model()),
+      zoom_callback_(base::Bind(&WrenchMenuModel::OnZoomLevelChanged,
+                                base::Unretained(this))) {
   Build(is_new_menu, supports_new_separators);
   UpdateZoomControls();
 
+  HostZoomMap::GetForBrowserContext(
+      browser->profile())->AddZoomLevelChangedCallback(zoom_callback_);
+
   tab_strip_model_->AddObserver(this);
 
-  registrar_.Add(
-      this, content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-      content::Source<HostZoomMap>(
-          HostZoomMap::GetForBrowserContext(browser_->profile())));
   registrar_.Add(this, content::NOTIFICATION_NAV_ENTRY_COMMITTED,
                  content::NotificationService::AllSources());
 }
@@ -229,6 +230,11 @@ WrenchMenuModel::WrenchMenuModel(ui::AcceleratorProvider* provider,
 WrenchMenuModel::~WrenchMenuModel() {
   if (tab_strip_model_)
     tab_strip_model_->RemoveObserver(this);
+
+  if (browser()) {
+    HostZoomMap::GetForBrowserContext(
+        browser()->profile())->RemoveZoomLevelChangedCallback(zoom_callback_);
+  }
 }
 
 bool WrenchMenuModel::DoesCommandIdDismissMenu(int command_id) const {
@@ -421,14 +427,8 @@ void WrenchMenuModel::TabStripModelDeleted() {
 void WrenchMenuModel::Observe(int type,
                               const content::NotificationSource& source,
                               const content::NotificationDetails& details) {
-  switch (type) {
-    case content::NOTIFICATION_ZOOM_LEVEL_CHANGED:
-    case content::NOTIFICATION_NAV_ENTRY_COMMITTED:
-      UpdateZoomControls();
-      break;
-    default:
-      NOTREACHED();
-  }
+  DCHECK(type == content::NOTIFICATION_NAV_ENTRY_COMMITTED);
+  UpdateZoomControls();
 }
 
 // For testing.
@@ -697,3 +697,7 @@ void WrenchMenuModel::UpdateZoomControls() {
   zoom_label_ = l10n_util::GetStringFUTF16(
       IDS_ZOOM_PERCENT, base::IntToString16(zoom_percent));
 }
+
+void WrenchMenuModel::OnZoomLevelChanged(const std::string& host) {
+  UpdateZoomControls();
+}
diff --git a/chrome/browser/ui/toolbar/wrench_menu_model.h b/chrome/browser/ui/toolbar/wrench_menu_model.h
index 21bbdc2..b78ab62 100644
--- a/chrome/browser/ui/toolbar/wrench_menu_model.h
+++ b/chrome/browser/ui/toolbar/wrench_menu_model.h
@@ -8,6 +8,7 @@
 #include "base/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/ui/tabs/tab_strip_model_observer.h"
+#include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "ui/base/accelerators/accelerator.h"
@@ -147,6 +148,8 @@ class WrenchMenuModel : public ui::SimpleMenuModel,
   // |new_menu| should be set to true.
   void CreateZoomMenu(bool new_menu);
 
+  void OnZoomLevelChanged(const std::string& host);
+
   // Models for the special menu items with buttons.
   scoped_ptr<ui::ButtonMenuItemModel> edit_menu_item_model_;
   scoped_ptr<ui::ButtonMenuItemModel> zoom_menu_item_model_;
@@ -168,6 +171,7 @@ class WrenchMenuModel : public ui::SimpleMenuModel,
   Browser* browser_;  // weak
   TabStripModel* tab_strip_model_; // weak
 
+  content::HostZoomMap::ZoomLevelChangedCallback zoom_callback_;
   content::NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(WrenchMenuModel);
diff --git a/chrome/browser/ui/views/wrench_menu.cc b/chrome/browser/ui/views/wrench_menu.cc
index c7b65df..2b2ad2a 100644
--- a/chrome/browser/ui/views/wrench_menu.cc
+++ b/chrome/browser/ui/views/wrench_menu.cc
@@ -480,8 +480,7 @@ static const int kTouchZoomPadding = 14;
 // ZoomView contains the various zoom controls: two buttons to increase/decrease
 // the zoom, a label showing the current zoom percent, and a button to go
 // full-screen.
-class WrenchMenu::ZoomView : public WrenchMenuView,
-                             public content::NotificationObserver {
+class WrenchMenu::ZoomView : public WrenchMenuView {
  public:
   ZoomView(WrenchMenu* menu,
            MenuModel* menu_model,
@@ -490,11 +489,17 @@ class WrenchMenu::ZoomView : public WrenchMenuView,
            int fullscreen_index)
       : WrenchMenuView(menu, menu_model),
         fullscreen_index_(fullscreen_index),
+        zoom_callback_(base::Bind(&WrenchMenu::ZoomView::OnZoomLevelChanged,
+                                  base::Unretained(this))),
         increment_button_(NULL),
         zoom_label_(NULL),
         decrement_button_(NULL),
         fullscreen_button_(NULL),
         zoom_label_width_(0) {
+    HostZoomMap::GetForBrowserContext(
+        menu_->browser_->profile())->AddZoomLevelChangedCallback(
+            zoom_callback_);
+
     decrement_button_ = CreateButtonWithAccName(
         IDS_ZOOM_MINUS2, MenuButtonBackground::LEFT_BUTTON, decrement_index,
         NULL, IDS_ACCNAME_ZOOM_MINUS2);
@@ -555,11 +560,12 @@ class WrenchMenu::ZoomView : public WrenchMenuView,
     AddChildView(fullscreen_button_);
 
     UpdateZoomControls();
+  }
 
-    registrar_.Add(
-        this, content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-        content::Source<HostZoomMap>(
-            HostZoomMap::GetForBrowserContext(menu->browser_->profile())));
+  ~ZoomView() {
+    HostZoomMap::GetForBrowserContext(
+        menu_->browser_->profile())->RemoveZoomLevelChangedCallback(
+            zoom_callback_);
   }
 
   // Overridden from View.
@@ -613,15 +619,11 @@ class WrenchMenu::ZoomView : public WrenchMenuView,
     }
   }
 
-  // Overridden from content::NotificationObserver.
-  virtual void Observe(int type,
-                       const content::NotificationSource& source,
-                       const content::NotificationDetails& details) OVERRIDE {
-    DCHECK_EQ(content::NOTIFICATION_ZOOM_LEVEL_CHANGED, type);
+ private:
+  void OnZoomLevelChanged(const std::string& host) {
     UpdateZoomControls();
   }
 
- private:
   void UpdateZoomControls() {
     bool enable_increment = false;
     bool enable_decrement = false;
@@ -669,6 +671,7 @@ class WrenchMenu::ZoomView : public WrenchMenuView,
   // Index of the fullscreen menu item in the model.
   const int fullscreen_index_;
 
+  content::HostZoomMap::ZoomLevelChangedCallback zoom_callback_;
   content::NotificationRegistrar registrar_;
 
   // Button for incrementing the zoom.
diff --git a/chrome/browser/ui/zoom/zoom_controller.cc b/chrome/browser/ui/zoom/zoom_controller.cc
index d17864f..4b9c041 100644
--- a/chrome/browser/ui/zoom/zoom_controller.cc
+++ b/chrome/browser/ui/zoom/zoom_controller.cc
@@ -24,7 +24,10 @@ DEFINE_WEB_CONTENTS_USER_DATA_KEY(ZoomController);
 ZoomController::ZoomController(content::WebContents* web_contents)
     : content::WebContentsObserver(web_contents),
       zoom_percent_(100),
-      observer_(NULL) {
+      observer_(NULL),
+      browser_context_(web_contents->GetBrowserContext()),
+      zoom_callback_(base::Bind(&ZoomController::OnZoomLevelChanged,
+                                base::Unretained(this))) {
   Profile* profile =
       Profile::FromBrowserContext(web_contents->GetBrowserContext());
   default_zoom_level_.Init(prefs::kDefaultZoomLevel, profile->GetPrefs(),
@@ -32,15 +35,18 @@ ZoomController::ZoomController(content::WebContents* web_contents)
                                       base::Unretained(this),
                                       std::string()));
 
-  content::HostZoomMap* zoom_map =
-      content::HostZoomMap::GetForBrowserContext(profile);
-  registrar_.Add(this, content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-                 content::Source<content::HostZoomMap>(zoom_map));
+  content::HostZoomMap::GetForBrowserContext(
+      browser_context_)->AddZoomLevelChangedCallback(
+          zoom_callback_);
 
   UpdateState(std::string());
 }
 
-ZoomController::~ZoomController() {}
+ZoomController::~ZoomController() {
+  content::HostZoomMap::GetForBrowserContext(
+      browser_context_)->RemoveZoomLevelChangedCallback(
+          zoom_callback_);
+}
 
 bool ZoomController::IsAtDefaultZoom() const {
   return content::ZoomValuesEqual(web_contents()->GetZoomLevel(),
@@ -61,11 +67,8 @@ void ZoomController::DidNavigateMainFrame(
   UpdateState(std::string());
 }
 
-void ZoomController::Observe(int type,
-                             const content::NotificationSource& source,
-                             const content::NotificationDetails& details) {
-  DCHECK_EQ(content::NOTIFICATION_ZOOM_LEVEL_CHANGED, type);
-  UpdateState(*content::Details<std::string>(details).ptr());
+void ZoomController::OnZoomLevelChanged(const std::string& host) {
+  UpdateState(host);
 }
 
 void ZoomController::UpdateState(const std::string& host) {
diff --git a/chrome/browser/ui/zoom/zoom_controller.h b/chrome/browser/ui/zoom/zoom_controller.h
index 1dd7809..2dda110 100644
--- a/chrome/browser/ui/zoom/zoom_controller.h
+++ b/chrome/browser/ui/zoom/zoom_controller.h
@@ -8,8 +8,7 @@
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/prefs/public/pref_member.h"
-#include "content/public/browser/notification_observer.h"
-#include "content/public/browser/notification_registrar.h"
+#include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
@@ -20,8 +19,7 @@ class WebContents;
 }
 
 // Per-tab class to manage the Omnibox zoom icon.
-class ZoomController : public content::NotificationObserver,
-                       public content::WebContentsObserver,
+class ZoomController : public content::WebContentsObserver,
                        public content::WebContentsUserData<ZoomController> {
  public:
   virtual ~ZoomController();
@@ -41,16 +39,13 @@ class ZoomController : public content::NotificationObserver,
       const content::LoadCommittedDetails& details,
       const content::FrameNavigateParams& params) OVERRIDE;
 
-  // content::NotificationObserver overrides:
-  virtual void Observe(int type,
-                       const content::NotificationSource& source,
-                       const content::NotificationDetails& details) OVERRIDE;
-
  private:
   explicit ZoomController(content::WebContents* web_contents);
   friend class content::WebContentsUserData<ZoomController>;
   friend class ZoomControllerTest;
 
+  void OnZoomLevelChanged(const std::string& host);
+
   // Updates the zoom icon and zoom percentage based on current values and
   // notifies the observer if changes have occurred. |host| may be empty,
   // meaning the change should apply to ~all sites. If it is not empty, the
@@ -60,14 +55,16 @@ class ZoomController : public content::NotificationObserver,
   // The current zoom percentage.
   int zoom_percent_;
 
-  content::NotificationRegistrar registrar_;
-
   // Used to access the default zoom level preference.
   DoublePrefMember default_zoom_level_;
 
   // Observer receiving notifications on state changes.
   ZoomObserver* observer_;
 
+  content::BrowserContext* browser_context_;
+
+  content::HostZoomMap::ZoomLevelChangedCallback zoom_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(ZoomController);
 };
 
diff --git a/chrome/browser/ui/zoom/zoom_controller_unittest.cc b/chrome/browser/ui/zoom/zoom_controller_unittest.cc
index cc5be54..f96cfb7 100644
--- a/chrome/browser/ui/zoom/zoom_controller_unittest.cc
+++ b/chrome/browser/ui/zoom/zoom_controller_unittest.cc
@@ -14,9 +14,6 @@
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/navigation_details.h"
-#include "content/public/browser/notification_details.h"
-#include "content/public/browser/notification_source.h"
-#include "content/public/browser/notification_types.h"
 #include "content/public/common/frame_navigate_params.h"
 #include "content/public/test/test_browser_thread.h"
 #include "content/public/test/test_utils.h"
@@ -71,11 +68,5 @@ TEST_F(ZoomControllerTest, Observe) {
       content::HostZoomMap::GetForBrowserContext(
           web_contents()->GetBrowserContext());
 
-  content::WindowedNotificationObserver notification_observer(
-      content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-      content::NotificationService::AllSources());
-
   host_zoom_map->SetZoomLevel(std::string(), 110.0f);
-
-  notification_observer.Wait();
 }
diff --git a/content/browser/host_zoom_map_impl.cc b/content/browser/host_zoom_map_impl.cc
index 942d6f4..aa5a870 100644
--- a/content/browser/host_zoom_map_impl.cc
+++ b/content/browser/host_zoom_map_impl.cc
@@ -90,10 +90,8 @@ void HostZoomMapImpl::SetZoomLevel(const std::string& host, double level) {
     }
   }
 
-  NotificationService::current()->Notify(
-      NOTIFICATION_ZOOM_LEVEL_CHANGED,
-      Source<HostZoomMap>(this),
-      Details<const std::string>(&host));
+  for (size_t i = 0; i < zoom_level_changed_callbacks_.size(); i++)
+    zoom_level_changed_callbacks_[i].Run(host);
 }
 
 double HostZoomMapImpl::GetDefaultZoomLevel() const {
@@ -104,6 +102,22 @@ void HostZoomMapImpl::SetDefaultZoomLevel(double level) {
   default_zoom_level_ = level;
 }
 
+void HostZoomMapImpl::AddZoomLevelChangedCallback(
+    const ZoomLevelChangedCallback& callback) {
+  zoom_level_changed_callbacks_.push_back(callback);
+}
+
+void HostZoomMapImpl::RemoveZoomLevelChangedCallback(
+    const ZoomLevelChangedCallback& callback) {
+  for (size_t i = 0; i < zoom_level_changed_callbacks_.size(); i++) {
+    if (zoom_level_changed_callbacks_[i].Equals(callback)) {
+      zoom_level_changed_callbacks_.erase(
+          zoom_level_changed_callbacks_.begin() + i);
+      return;
+    }
+  }
+}
+
 double HostZoomMapImpl::GetTemporaryZoomLevel(int render_process_id,
                                               int render_view_id) const {
   base::AutoLock auto_lock(lock_);
@@ -145,11 +159,8 @@ void HostZoomMapImpl::SetTemporaryZoomLevel(int render_process_id,
     }
   }
 
-  std::string host;
-  NotificationService::current()->Notify(
-      NOTIFICATION_ZOOM_LEVEL_CHANGED,
-      Source<HostZoomMap>(this),
-      Details<const std::string>(&host));
+  for (size_t i = 0; i < zoom_level_changed_callbacks_.size(); i++)
+    zoom_level_changed_callbacks_[i].Run(std::string());
 }
 
 void HostZoomMapImpl::Observe(int type,
diff --git a/content/browser/host_zoom_map_impl.h b/content/browser/host_zoom_map_impl.h
index 7840188..4e6eff4 100644
--- a/content/browser/host_zoom_map_impl.h
+++ b/content/browser/host_zoom_map_impl.h
@@ -34,6 +34,10 @@ class CONTENT_EXPORT HostZoomMapImpl : public NON_EXPORTED_BASE(HostZoomMap),
   virtual void SetZoomLevel(const std::string& host, double level) OVERRIDE;
   virtual double GetDefaultZoomLevel() const OVERRIDE;
   virtual void SetDefaultZoomLevel(double level) OVERRIDE;
+  virtual void AddZoomLevelChangedCallback(
+      const ZoomLevelChangedCallback& callback) OVERRIDE;
+  virtual void RemoveZoomLevelChangedCallback(
+      const ZoomLevelChangedCallback& callback) OVERRIDE;
 
   // Returns the temporary zoom level that's only valid for the lifetime of
   // the given WebContents (i.e. isn't saved and doesn't affect other
@@ -59,6 +63,9 @@ class CONTENT_EXPORT HostZoomMapImpl : public NON_EXPORTED_BASE(HostZoomMap),
  private:
   typedef std::map<std::string, double> HostZoomLevels;
 
+  // Callbacks called when zoom level changes.
+  std::vector<ZoomLevelChangedCallback> zoom_level_changed_callbacks_;
+
   // Copy of the pref data, so that we can read it on the IO thread.
   HostZoomLevels host_zoom_levels_;
   double default_zoom_level_;
diff --git a/content/public/browser/host_zoom_map.h b/content/public/browser/host_zoom_map.h
index 1e32e79..c399f69 100644
--- a/content/public/browser/host_zoom_map.h
+++ b/content/public/browser/host_zoom_map.h
@@ -10,6 +10,7 @@
 #include <vector>
 
 #include "base/basictypes.h"
+#include "base/callback.h"
 #include "content/common/content_export.h"
 
 namespace content {
@@ -50,6 +51,14 @@ class HostZoomMap {
   virtual double GetDefaultZoomLevel() const = 0;
   virtual void SetDefaultZoomLevel(double level) = 0;;
 
+  typedef base::Callback<void(const std::string&)> ZoomLevelChangedCallback;
+
+  // Add and remove zoom level changed callbacks.
+  virtual void AddZoomLevelChangedCallback(
+      const ZoomLevelChangedCallback& callback) = 0;
+  virtual void RemoveZoomLevelChangedCallback(
+      const ZoomLevelChangedCallback& callback) = 0;
+
  protected:
   virtual ~HostZoomMap() {}
 };
diff --git a/content/public/browser/notification_types.h b/content/public/browser/notification_types.h
index ced9dcf..4c3bd71 100644
--- a/content/public/browser/notification_types.h
+++ b/content/public/browser/notification_types.h
@@ -336,11 +336,6 @@ enum NotificationType {
   // The source is a NavigationController.
   NOTIFICATION_REPOST_WARNING_SHOWN,
 
-  // Sent when the zoom level changes. The source is the HostZoomMap.  The
-  // details is a string of the hostname for which the zoom changed.  In case
-  // of a temporary zoom level change, the details is an empty string.
-  NOTIFICATION_ZOOM_LEVEL_CHANGED,
-
   // Custom notifications used by the embedder should start from here.
   NOTIFICATION_CONTENT_END,
 };