content: convert zoom notifications to observer usage

chrome/browser/ui/toolbar/wrench_menu_model.h

Index: chrome/browser/ui/toolbar/wrench_menu_model.h
diff --git a/chrome/browser/ui/toolbar/wrench_menu_model.h b/chrome/browser/ui/toolbar/wrench_menu_model.h
index 33992881fb36fbb57cc4ca10f7a3f3e43fc84702..af0c8e16bb9e9765903bfe6385646e556b597188 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"
@@ -154,6 +155,8 @@ class WrenchMenuModel : public ui::SimpleMenuModel,
   // messages.
   GlobalError* GetActiveSignedInServiceError() const;
 
+  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_;
@@ -175,6 +178,7 @@ 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);