ui: Cleanup class/struct forward declarations

ui/message_center/message_center.h

 // Copyright (c) 2012 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_H_
 #define UI_MESSAGE_CENTER_MESSAGE_CENTER_H_
 
 #include <stddef.h>
 
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "ui/message_center/message_center_export.h"
 #include "ui/message_center/message_center_types.h"
 #include "ui/message_center/notification_list.h"
 
 class DownloadNotification;
 class DownloadNotificationTestBase;
 
-namespace base {
-class DictionaryValue;
-}
-
 // Interface to manage the NotificationList. The client (e.g. Chrome) calls
 // [Add|Remove|Update]Notification to create and update notifications in the
 // list. It also sends those changes to its observers when a notification
 // is shown, closed, or clicked on.
 //
 // MessageCenter is agnostic of profiles; it uses the string returned by
 // message_center::Notification::id() to uniquely identify a notification. It is
 // the caller's responsibility to formulate the id so that 2 different
 // notification should have different ids. For example, if the caller supports
 // multiple profiles, then caller should encode both profile characteristics and
@@ skipping 180 matching lines @@
   // Note carefully: this may break the layout of message center. Shouldn't use
   // this method if the update changes its notification size.
   virtual void ForceNotificationFlush(const std::string& id) {}
 
   DISALLOW_COPY_AND_ASSIGN(MessageCenter);
 };
 
 }  // namespace message_center
 
 #endif  // UI_MESSAGE_CENTER_MESSAGE_CENTER_H_