ash: Cleanup class/struct forward declarations

ash/mus/window_manager_application.h

 // Copyright 2015 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_MUS_WINDOW_MANAGER_APPLICATION_H_
 #define ASH_MUS_WINDOW_MANAGER_APPLICATION_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 17 matching lines @@
 class ScopedFakeStatisticsProvider;
 }
 }
 
 namespace views {
 class AuraInit;
 class SurfaceContextFactory;
 }
 
 namespace ui {
-class Event;
 class GpuService;
 class WindowTreeClient;
 }
 
 namespace ash {
 namespace mus {
 
 class NativeWidgetFactoryMus;
 class NetworkConnectDelegateMus;
 class WindowManager;
@@ skipping 53 matching lines @@
       statistics_provider_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(WindowManagerApplication);
 };
 
 }  // namespace mus
 }  // namespace ash
 
 #endif  // ASH_MUS_WINDOW_MANAGER_APPLICATION_H_