ash: Cleanup class/struct forward declarations

ash/wm/boot_splash_screen_chromeos.h

 // Copyright 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 ASH_WM_BOOT_SPLASH_SCREEN_CHROMEOS_H_
 #define ASH_WM_BOOT_SPLASH_SCREEN_CHROMEOS_H_
 
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "base/time/time.h"
 
 namespace aura {
 class WindowTreeHost;
 }
 
 namespace ui {
 class Layer;
-class LayerDelegate;
 }
 
 namespace ash {
 
 // BootSplashScreen manages a ui::Layer, stacked at the top of the root layer's
 // children, that displays a copy of the initial contents of the host window.
 // This allows us to continue displaying the Chrome OS boot splash screen (which
 // is displayed before Ash starts) after the compositor has taken over so we can
 // animate the transition between the splash screen and the login screen.
 class BootSplashScreen {
@@ skipping 11 matching lines @@
   std::unique_ptr<CopyHostContentLayerDelegate> layer_delegate_;
 
   std::unique_ptr<ui::Layer> layer_;
 
   DISALLOW_COPY_AND_ASSIGN(BootSplashScreen);
 };
 
 }  // namespace ash
 
 #endif  // ASH_WM_BOOT_SPLASH_SCREEN_CHROMEOS_H_