Remove content::NotificationObserver dependency from most Prefs code.

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 ffc2a78fe0373aca4bfdc05129fb3bb49f198c82..f7aed95ba46d1245da291190d5523d918b8fa379 100644
--- a/chrome/browser/ui/zoom/zoom_controller.h
+++ b/chrome/browser/ui/zoom/zoom_controller.h
@@ -7,6 +7,7 @@
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
+#include "base/prefs/public/pref_observer.h"
 #include "chrome/browser/api/prefs/pref_member.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
@@ -21,6 +22,7 @@ class WebContents;
 
 // Per-tab class to manage the Omnibox zoom icon.
 class ZoomController : public content::NotificationObserver,
+                       public PrefObserver,
                        public content::WebContentsObserver,
                        public content::WebContentsUserData<ZoomController> {
  public:
@@ -50,6 +52,10 @@ class ZoomController : public content::NotificationObserver,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // PrefObserver overrides:
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
   // Updates the zoom icon and zoom percentage based on current values and
   // notifies the observer if changes have occurred. |host| may be empty,
   // meaning the change should apply to ~all sites. If it is not empty, the