content: convert zoom notifications to observer usage

chrome/browser/ui/zoom/zoom_controller.h

Index: chrome/browser/ui/zoom/zoom_controller.h
diff --git a/chrome/browser/ui/zoom/zoom_controller.h b/chrome/browser/ui/zoom/zoom_controller.h
index 1dd7809c84c59acb7ebbfbf7f5bb0bf95d1ff318..bcdd8e6a05d62a9e5c4f4bc0d77c40d4437cd678 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"
 
@@ -20,7 +19,7 @@ class WebContents;
 }
 
 // Per-tab class to manage the Omnibox zoom icon.
-class ZoomController : public content::NotificationObserver,
+class ZoomController : public content::HostZoomMap::Observer,
                        public content::WebContentsObserver,
                        public content::WebContentsUserData<ZoomController> {
  public:
@@ -36,16 +35,14 @@ class ZoomController : public content::NotificationObserver,
 
   void set_observer(ZoomObserver* observer) { observer_ = observer; }
 
+  // content::HostZoomMap::Observer overrides:
+  virtual void OnZoomLevelChanged(const std::string& host) OVERRIDE;
+
   // content::WebContentsObserver overrides:
   virtual void DidNavigateMainFrame(
       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>;
@@ -60,8 +57,6 @@ 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_;