Implement GpuArcVideoService::AcceleratorStub using mojo

content/common/gpu/gpu_channel_manager.h

Index: content/common/gpu/gpu_channel_manager.h
diff --git a/content/common/gpu/gpu_channel_manager.h b/content/common/gpu/gpu_channel_manager.h
index f195a55c27e05d38d084fa1bccbd7ec530eb1d57..f9dfbebf137022dae70dd44d85e321ff2902062d 100644
--- a/content/common/gpu/gpu_channel_manager.h
+++ b/content/common/gpu/gpu_channel_manager.h
@@ -59,7 +59,9 @@ struct GpuMsg_EstablishChannel_Params;
 
 namespace content {
 #if defined(OS_CHROMEOS)
+namespace arc {
 class GpuArcVideoService;
+}  // namespace arc
 #endif
 class GpuChannel;
 class GpuMemoryBufferFactory;
@@ -204,7 +206,7 @@ class CONTENT_EXPORT GpuChannelManager : public IPC::Listener,
       framebuffer_completeness_cache_;
   scoped_refptr<gfx::GLSurface> default_offscreen_surface_;
 #if defined(OS_CHROMEOS)
-  scoped_ptr<GpuArcVideoService> gpu_arc_video_service_;
+  scoped_ptr<arc::GpuArcVideoService> gpu_arc_video_service_;
 #endif
   GpuMemoryBufferFactory* const gpu_memory_buffer_factory_;
 #if defined(OS_ANDROID)