ui: Cleanup class/struct forward declarations

ui/aura/mus/window_compositor_frame_sink.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 UI_AURA_MUS_WINDOW_COMPOSITOR_FRAME_SINK_H_
 #define UI_AURA_MUS_WINDOW_COMPOSITOR_FRAME_SINK_H_
 
 #include "base/macros.h"
 #include "cc/ipc/mojo_compositor_frame_sink.mojom.h"
 #include "cc/output/compositor_frame_sink.h"
 #include "cc/scheduler/begin_frame_source.h"
 #include "cc/surfaces/surface_id.h"
 #include "mojo/public/cpp/bindings/binding.h"
 
-namespace gpu {
-class GpuChannelHost;
-}
-
 namespace aura {
 
 class WindowCompositorFrameSinkBinding;
 
 class WindowCompositorFrameSink
     : public cc::CompositorFrameSink,
       public cc::mojom::MojoCompositorFrameSinkClient,
       public cc::ExternalBeginFrameSourceClient {
  public:
   // static
@@ skipping 61 matching lines @@
   cc::mojom::MojoCompositorFrameSinkRequest compositor_frame_sink_request_;
   mojo::InterfacePtrInfo<cc::mojom::MojoCompositorFrameSinkClient>
       compositor_frame_sink_client_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowCompositorFrameSinkBinding);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_COMPOSITOR_FRAME_SINK_H_