gpu: Cleanup class/struct forward declarations

gpu/ipc/service/pass_through_image_transport_surface.h

 // Copyright 2016 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_PASS_THROUGH_IMAGE_TRANSPORT_SURFACE_H_
 #define GPU_IPC_SERVICE_PASS_THROUGH_IMAGE_TRANSPORT_SURFACE_H_
 
 #include <stdint.h>
 
 #include <memory>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "gpu/ipc/service/image_transport_surface.h"
 #include "gpu/ipc/service/image_transport_surface_delegate.h"
 #include "ui/events/latency_info.h"
 #include "ui/gl/gl_surface.h"
 
 namespace gpu {
-class GpuChannelManager;
 
 // An implementation of ImageTransportSurface that implements GLSurface through
 // GLSurfaceAdapter, thereby forwarding GLSurface methods through to it.
 class PassThroughImageTransportSurface : public gl::GLSurfaceAdapter {
  public:
   PassThroughImageTransportSurface(
       base::WeakPtr<ImageTransportSurfaceDelegate> delegate,
       gl::GLSurface* surface);
 
   // GLSurface implementation.
@@ skipping 37 matching lines @@
   bool did_set_swap_interval_;
   std::vector<ui::LatencyInfo> latency_info_;
   base::WeakPtrFactory<PassThroughImageTransportSurface> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PassThroughImageTransportSurface);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_IPC_SERVICE_PASS_THROUGH_IMAGE_TRANSPORT_SURFACE_H_