chrome: Cleanup class/struct forward declarations

chrome/browser/status_icons/desktop_notification_balloon.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 CHROME_BROWSER_STATUS_ICONS_DESKTOP_NOTIFICATION_BALLOON_H_
 #define CHROME_BROWSER_STATUS_ICONS_DESKTOP_NOTIFICATION_BALLOON_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/strings/string16.h"
 
-class Notification;
 class Profile;
 
 namespace gfx {
 class ImageSkia;
 }
 
 namespace message_center {
 struct NotifierId;
 }
 
@@ skipping 13 matching lines @@
   std::string notification_id_;
   Profile* profile_;
 
   // Counter to provide unique ids to notifications.
   static int id_count_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopNotificationBalloon);
 };
 
 #endif  // CHROME_BROWSER_STATUS_ICONS_DESKTOP_NOTIFICATION_BALLOON_H_