content: convert zoom notifications to observer usage

chrome/browser/profiles/profile_impl.h

Index: chrome/browser/profiles/profile_impl.h
diff --git a/chrome/browser/profiles/profile_impl.h b/chrome/browser/profiles/profile_impl.h
index d25fae4dde552707ec686f07d993247f09b91a98..d1c8b2e6f95ea7cf9907b9cf17688cae850a2273 100644
--- a/chrome/browser/profiles/profile_impl.h
+++ b/chrome/browser/profiles/profile_impl.h
@@ -17,6 +17,7 @@
 #include "base/timer.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_impl_io_data.h"
+#include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
@@ -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);
@@ -192,6 +194,7 @@ class ProfileImpl : public Profile,
   virtual base::Callback<ChromeURLDataManagerBackend*(void)>
       GetChromeURLDataManagerBackendGetter() const OVERRIDE;
 
+  content::HostZoomMap::ZoomLevelChangedCallback zoom_callback_;
   content::NotificationRegistrar registrar_;
   PrefChangeRegistrar pref_change_registrar_;