ash: Cleanup class/struct forward declarations

ash/host/ash_window_tree_host_x11.h

 // Copyright 2014 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_HOST_ASH_WINDOW_TREE_HOST_X11_H_
 #define ASH_HOST_ASH_WINDOW_TREE_HOST_X11_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
 #include "ash/host/ash_window_tree_host.h"
 #include "ash/host/transformer_helper.h"
 #include "base/macros.h"
 #include "ui/aura/env_observer.h"
 #include "ui/aura/window_tree_host_x11.h"
 
 namespace ash {
 class RootWindowTransformer;
-class MouseCursorEventFilter;
 
 class ASH_EXPORT AshWindowTreeHostX11 : public AshWindowTreeHost,
                                         public aura::WindowTreeHostX11,
                                         public aura::EnvObserver {
  public:
   explicit AshWindowTreeHostX11(const gfx::Rect& initial_bounds);
   ~AshWindowTreeHostX11() override;
 
  private:
   // AshWindowTreeHost:
@@ skipping 36 matching lines @@
   std::unique_ptr<XID[]> pointer_barriers_;
 
   TransformerHelper transformer_helper_;
 
   DISALLOW_COPY_AND_ASSIGN(AshWindowTreeHostX11);
 };
 
 }  // namespace ash
 
 #endif  // ASH_HOST_ASH_WINDOW_TREE_HOST_X11_H_