Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/notifications/notification_ui_manager_impl.h

Index: chrome/browser/notifications/notification_ui_manager_impl.h
diff --git a/chrome/browser/notifications/notification_ui_manager_impl.h b/chrome/browser/notifications/notification_ui_manager_impl.h
index e3136228aec1e55985c34e99e9a1de6542d50722..0adebdfb88b4cf1f738ab7751ef8ceb4884d98ce 100644
--- a/chrome/browser/notifications/notification_ui_manager_impl.h
+++ b/chrome/browser/notifications/notification_ui_manager_impl.h
@@ -11,6 +11,7 @@
 
 #include "base/id_map.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/prefs/public/pref_observer.h"
 #include "base/timer.h"
 #include "chrome/browser/api/prefs/pref_member.h"
 #include "chrome/browser/notifications/balloon.h"
@@ -31,7 +32,8 @@ class NotificationUIManagerImpl
     : public NotificationUIManager,
       public NotificationPrefsManager,
       public BalloonCollection::BalloonSpaceChangeListener,
-      public content::NotificationObserver {
+      public content::NotificationObserver,
+      public PrefObserver {
  public:
   explicit NotificationUIManagerImpl(PrefService* local_state);
   virtual ~NotificationUIManagerImpl();
@@ -63,6 +65,10 @@ class NotificationUIManagerImpl
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // PrefObserver override.
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
   // Attempts to display notifications from the show_queue if the user
   // is active.
   void CheckAndShowNotifications();