content: convert zoom notifications to observer usage

chrome/browser/ui/toolbar/wrench_menu_model.cc

Index: chrome/browser/ui/toolbar/wrench_menu_model.cc
diff --git a/chrome/browser/ui/toolbar/wrench_menu_model.cc b/chrome/browser/ui/toolbar/wrench_menu_model.cc
index 228c7ef63356f2dfb5e0993986d70135f9fd4a23..d81d5d53eeca58fe572d925dbb3fad86d6e2708e 100644
--- a/chrome/browser/ui/toolbar/wrench_menu_model.cc
+++ b/chrome/browser/ui/toolbar/wrench_menu_model.cc
@@ -223,6 +223,8 @@ WrenchMenuModel::WrenchMenuModel(ui::AcceleratorProvider* provider,
                                  bool is_new_menu,
                                  bool supports_new_separators)
     : ALLOW_THIS_IN_INITIALIZER_LIST(ui::SimpleMenuModel(this)),
+      content::HostZoomMap::Observer(
+        HostZoomMap::GetForBrowserContext(browser->profile())),
       provider_(provider),
       browser_(browser),
       tab_strip_model_(browser_->tab_strip_model()) {
@@ -231,10 +233,6 @@ WrenchMenuModel::WrenchMenuModel(ui::AcceleratorProvider* provider,
 
   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());
 }
@@ -452,17 +450,15 @@ void WrenchMenuModel::TabStripModelDeleted() {
   tab_strip_model_ = NULL;
 }
 
+void WrenchMenuModel::OnZoomLevelChanged(const std::string& host) {
+  UpdateZoomControls();
+}
+
 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.