ash: Cleanup class/struct forward declarations

ash/wm/window_properties.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_WM_WINDOW_PROPERTIES_H_
 #define ASH_WM_WINDOW_PROPERTIES_H_
 
 #include "ash/ash_export.h"
 #include "ash/common/shelf/shelf_item_types.h"
 #include "ui/base/ui_base_types.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace aura {
-class Window;
-
 template <typename T>
 struct WindowProperty;
 }
 
 namespace ash {
 namespace wm {
 class WindowState;
 }  // namespace wm
 
 // Shell-specific window property keys.
@@ skipping 32 matching lines @@
 
 // A property key to store WindowState in the window. The window state
 // is owned by the window.
 extern const aura::WindowProperty<wm::WindowState*>* const kWindowStateKey;
 
 // Alphabetical sort.
 
 }  // namespace ash
 
 #endif  // ASH_WM_WINDOW_PROPERTIES_H_