ui: Cleanup class/struct forward declarations

ui/message_center/fake_message_center.h

 // Copyright 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_FAKE_MESSAGE_CENTER_H_
 #define UI_MESSAGE_CENTER_FAKE_MESSAGE_CENTER_H_
 
 #include <stddef.h>
 
 #include "base/macros.h"
 #include "ui/message_center/message_center.h"
 #include "ui/message_center/message_center_types.h"
 
 namespace message_center {
 
-class NotificationDelegate;
-
 // MessageCenter implementation of doing nothing. Useful for tests.
 class FakeMessageCenter : public MessageCenter {
  public:
   FakeMessageCenter();
   ~FakeMessageCenter() override;
 
   // Overridden from FakeMessageCenter.
   void AddObserver(MessageCenterObserver* observer) override;
   void RemoveObserver(MessageCenterObserver* observer) override;
   void AddNotificationBlocker(NotificationBlocker* blocker) override;
@@ skipping 49 matching lines @@
 
  private:
   const NotificationList::Notifications empty_notifications_;
 
   DISALLOW_COPY_AND_ASSIGN(FakeMessageCenter);
 };
 
 }  // namespace message_center
 
 #endif  // UI_MESSAGE_CENTER_FAKE_MESSAGE_CENTER_H_