ui: Cleanup class/struct forward declarations

ui/message_center/message_center_tray.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_TRAY_H_
 #define UI_MESSAGE_CENTER_MESSAGE_CENTER_TRAY_H_
 
 #include "base/macros.h"
 #include "base/observer_list.h"
 #include "base/strings/string16.h"
 #include "ui/message_center/message_center_export.h"
 #include "ui/message_center/message_center_observer.h"
 #include "ui/message_center/message_center_tray_delegate.h"
 #include "ui/message_center/notifier_settings.h"
 
 namespace ui {
 class MenuModel;
 }
 
 namespace message_center {
 
 class MessageCenter;
-class MessageBubbleBase;
-class MessagePopupBubble;
-class QuietModeBubble;
 
 // Implementation found with each supported platform's implementation of
 // MessageCenterTrayDelegate.
 MessageCenterTrayDelegate* CreateMessageCenterTray();
 
 // Class that observes a MessageCenter. Manages the popup and message center
 // bubbles. Tells the MessageCenterTrayHost when the tray is changed, as well
 // as when bubbles are shown and hidden.
 class MESSAGE_CENTER_EXPORT MessageCenterTray : public MessageCenterObserver {
  public:
@@ skipping 61 matching lines @@
   bool popups_visible_;
   // |delegate_| is a weak pointer that must live longer than MessageCenterTray.
   MessageCenterTrayDelegate* delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageCenterTray);
 };
 
 }  // namespace message_center
 
 #endif  // UI_MESSAGE_CENTER_MESSAGE_CENTER_TRAY_H_