ash: Cleanup class/struct forward declarations

ash/common/system/tray/tray_background_view.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 ASH_COMMON_SYSTEM_TRAY_TRAY_BACKGROUND_VIEW_H_
 #define ASH_COMMON_SYSTEM_TRAY_TRAY_BACKGROUND_VIEW_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
 #include "ash/common/shelf/shelf_background_animator_observer.h"
 #include "ash/common/system/tray/actionable_view.h"
 #include "ash/public/cpp/shelf_types.h"
 #include "base/macros.h"
 #include "ui/compositor/layer_animation_observer.h"
 #include "ui/gfx/geometry/insets.h"
 #include "ui/views/bubble/tray_bubble_view.h"
 
 namespace ash {
-class ShelfLayoutManager;
 class TrayEventFilter;
 class TrayBackground;
 class WmShelf;
 
 // Base class for children of StatusAreaWidget: SystemTray, WebNotificationTray,
 // LogoutButtonTray, OverviewButtonTray.
 // This class handles setting and animating the background when the Launcher
 // is shown/hidden. It also inherits from ActionableView so that the tray
 // items can override PerformAction when clicked on.
 class ASH_EXPORT TrayBackgroundView : public ActionableView,
@@ skipping 159 matching lines @@
 
   std::unique_ptr<TrayWidgetObserver> widget_observer_;
   std::unique_ptr<TrayEventFilter> tray_event_filter_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayBackgroundView);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TRAY_TRAY_BACKGROUND_VIEW_H_