ui: Cleanup class/struct forward declarations

ui/message_center/message_center_impl.h

 // 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.
 
 #ifndef UI_MESSAGE_CENTER_MESSAGE_CENTER_IMPL_H_
 #define UI_MESSAGE_CENTER_MESSAGE_CENTER_IMPL_H_
 
 #include <stddef.h>
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "ui/message_center/message_center.h"
 #include "ui/message_center/message_center_observer.h"
 #include "ui/message_center/message_center_types.h"
 #include "ui/message_center/notification_blocker.h"
 #include "ui/message_center/notifier_settings.h"
 #include "ui/message_center/popup_timers_controller.h"
 
 namespace message_center {
-class NotificationDelegate;
 class MessageCenterImpl;
 
 namespace internal {
 class ChangeQueue;
 }
 
 // The default implementation of MessageCenter.
 class MessageCenterImpl : public MessageCenter,
                           public NotificationBlocker::Observer,
                           public message_center::NotifierSettingsObserver {
@@ skipping 97 matching lines @@
   // Queue for the notifications to delay the addition/updates when the message
   // center is visible.
   std::unique_ptr<internal::ChangeQueue> notification_queue_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageCenterImpl);
 };
 
 }  // namespace message_center
 
 #endif  // UI_MESSAGE_CENTER_MESSAGE_CENTER_H_