[Mac][MC] Implement notification updates and relayouts.

ui/message_center/cocoa/popup_controller.mm

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ui/message_center/cocoa/popup_controller.h"
 
 #import "ui/base/cocoa/window_size_constants.h"
 #import "ui/message_center/cocoa/notification_controller.h"
 #include "ui/message_center/message_center.h"
 
@@ skipping 25 matching lines @@
         NSWindowCollectionBehaviorIgnoresCycle |
         NSWindowCollectionBehaviorFullScreenAuxiliary];
 
     [window setHasShadow:YES];
     [window setFrame:[[notificationController_ view] frame] display:NO];
     [window setContentView:[notificationController_ view]];
   }
   return self;
 }
 
+- (MCNotificationController*)notificationController {
+  return notificationController_.get();
+}
+
 - (const message_center::Notification*)notification {
   return [notificationController_ notification];
 }
 
 - (const std::string&)notificationID {
   return [notificationController_ notificationID];
 }
 
 @end