Start delegating notifications to MessageCenter on Windows.

ui/message_center/message_center.h

Index: ui/message_center/message_center.h
diff --git a/ui/message_center/message_center.h b/ui/message_center/message_center.h
index ff7eb0310d8b8d5356b5f89bd506ca9134dfbbf7..1c88569c962fb4bb180d5bd3e5bd49595cfd0254 100644
--- a/ui/message_center/message_center.h
+++ b/ui/message_center/message_center.h
@@ -74,8 +74,7 @@ class MESSAGE_CENTER_EXPORT MessageCenter : public NotificationList::Delegate {
     virtual ~Delegate() {}
   };
 
-  static MessageCenter* GetInstance();
-
+  MessageCenter();
   virtual ~MessageCenter();
 
   // Called to set the delegate.  Generally called only once, except in tests.
@@ -146,9 +145,6 @@ class MESSAGE_CENTER_EXPORT MessageCenter : public NotificationList::Delegate {
   virtual NotificationList* GetNotificationList() OVERRIDE;
 
  private:
-  friend struct DefaultSingletonTraits<MessageCenter>;
-  MessageCenter();
-
   // Calls OnMessageCenterChanged on each observer.
   void NotifyMessageCenterChanged(bool new_notification);