Add ArcGpuVideoDecodeAccelerator.

chrome/gpu/BUILD.gn

 # 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.
 
 static_library("gpu") {
   deps = [
     "//content/public/common",
     "//content/public/gpu",
   ]
 
   sources = [
     "chrome_content_gpu_client.cc",
     "chrome_content_gpu_client.h",
   ]
 
   if (is_chromeos) {
     deps += [ "//components/arc:arc_bindings" ]
     sources += [
+      "arc_gpu_video_decode_accelerator.cc",
+      "arc_gpu_video_decode_accelerator.h",
       "arc_video_accelerator.h",
       "gpu_arc_video_service.cc",
       "gpu_arc_video_service.h",
     ]
   }
 }