content: convert zoom notifications to observer usage

chrome/browser/ui/gtk/browser_toolbar_gtk.h

Index: chrome/browser/ui/gtk/browser_toolbar_gtk.h
diff --git a/chrome/browser/ui/gtk/browser_toolbar_gtk.h b/chrome/browser/ui/gtk/browser_toolbar_gtk.h
index 932d142815695ada8b7ff483f3135d808636dc0e..5b3733e5359f74c10aa9e89478870b52fa0a6761 100644
--- a/chrome/browser/ui/gtk/browser_toolbar_gtk.h
+++ b/chrome/browser/ui/gtk/browser_toolbar_gtk.h
@@ -15,6 +15,7 @@
 #include "chrome/browser/ui/gtk/custom_button.h"
 #include "chrome/browser/ui/gtk/menu_gtk.h"
 #include "chrome/browser/ui/toolbar/wrench_menu_model.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"
@@ -43,6 +44,7 @@ class WebContents;
 class BrowserToolbarGtk : public CommandObserver,
                           public ui::AcceleratorProvider,
                           public MenuGtk::Delegate,
+                          public content::HostZoomMap::Observer,
                           public content::NotificationObserver {
  public:
   BrowserToolbarGtk(Browser* browser, BrowserWindowGtk* window);
@@ -99,6 +101,9 @@ class BrowserToolbarGtk : public CommandObserver,
       int id,
       ui::Accelerator* accelerator) OVERRIDE;
 
+  // content::HostZoomMap::Observer implementation:
+  virtual void OnZoomLevelChanged(const std::string& host) OVERRIDE;
+
   // content::NotificationObserver implementation.
   virtual void Observe(int type,
                        const content::NotificationSource& source,