gpu: Cleanup class/struct forward declarations

gpu/ipc/service/image_transport_surface.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 GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_H_
 #define GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_H_
 
 #include <stdint.h>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "build/build_config.h"
 #include "gpu/gpu_export.h"
 #include "gpu/ipc/common/surface_handle.h"
 #include "ui/gl/gl_surface.h"
 
 namespace gpu {
-class GpuChannelManager;
 class ImageTransportSurfaceDelegate;
 
 // The GPU process is agnostic as to how it displays results. On some platforms
 // it renders directly to window. On others it renders offscreen and transports
 // the results to the browser process to display. This file provides a simple
 // framework for making the offscreen path seem more like the onscreen path.
 
 class ImageTransportSurface {
  public:
 #if defined(OS_MACOSX)
   GPU_EXPORT static void SetAllowOSMesaForTesting(bool allow);
 #endif
 
   // Creates the appropriate native surface depending on the GL implementation.
   // This will be implemented separately by each platform. On failure, a null
   // scoped_refptr should be returned.
   static scoped_refptr<gl::GLSurface> CreateNativeSurface(
       base::WeakPtr<ImageTransportSurfaceDelegate> stub,
       SurfaceHandle surface_handle,
       gl::GLSurface::Format format);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ImageTransportSurface);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_H_