content: convert zoom notifications to observer usage

chrome/browser/ui/gtk/browser_toolbar_gtk.cc

Index: chrome/browser/ui/gtk/browser_toolbar_gtk.cc
diff --git a/chrome/browser/ui/gtk/browser_toolbar_gtk.cc b/chrome/browser/ui/gtk/browser_toolbar_gtk.cc
index 11e1b2b34b78916bd15475979e0b4f690ec2013a..84765b7a0520dbf7f1919028ff20b51ec5025420 100644
--- a/chrome/browser/ui/gtk/browser_toolbar_gtk.cc
+++ b/chrome/browser/ui/gtk/browser_toolbar_gtk.cc
@@ -241,9 +241,8 @@ 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)));
+  content::HostZoomMap::Observer::Observe(
+      HostZoomMap::GetForBrowserContext(profile));
 
   if (ShouldOnlyShowLocation()) {
     gtk_widget_show(event_box_);
@@ -372,6 +371,21 @@ bool BrowserToolbarGtk::GetAcceleratorForCommandId(
   return true;
 }
 
+// content::HostZoomMap::Observer ----------------------------------------------
+
+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();
+}
+
 // content::NotificationObserver -----------------------------------------------
 
 void BrowserToolbarGtk::Observe(int type,
@@ -416,18 +430,6 @@ 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();
   }