Start delegating notifications to MessageCenter on Windows.

ash/system/web_notification/web_notification_tray.h

Index: ash/system/web_notification/web_notification_tray.h
diff --git a/ash/system/web_notification/web_notification_tray.h b/ash/system/web_notification/web_notification_tray.h
index 0ecd334726bdbee3245912f55df022d8098c39d7..2e15ea793a9706e5c1442d5a1bb389f5dabfa411 100644
--- a/ash/system/web_notification/web_notification_tray.h
+++ b/ash/system/web_notification/web_notification_tray.h
@@ -74,7 +74,7 @@ class ASH_EXPORT WebNotificationTray
   bool IsMouseInNotificationBubble() const;
 
   message_center::MessageCenter* message_center() {
-    return message_center_;
+    return message_center_.get();
   }
 
   // Overridden from TrayBackgroundView.
@@ -155,7 +155,7 @@ class ASH_EXPORT WebNotificationTray
   message_center::MessageCenterBubble* GetMessageCenterBubbleForTest();
   message_center::MessagePopupBubble* GetPopupBubbleForTest();
 
-  message_center::MessageCenter* message_center_;
+  scoped_ptr<message_center::MessageCenter> message_center_;
   scoped_ptr<internal::WebNotificationBubbleWrapper> message_center_bubble_;
   scoped_ptr<internal::WebNotificationBubbleWrapper> popup_bubble_;
   scoped_ptr<message_center::QuietModeBubble> quiet_mode_bubble_;