Add ArcGpuVideoDecodeAccelerator.

chrome/chrome_gpu.gypi

 # 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.
 
 {
   'targets': [
     {
       # GN version: //chrome/gpu
       'target_name': 'gpu',
       'type': 'static_library',
       'include_dirs': [
         '..',
         '<(grit_out_dir)',
       ],
       'sources': [
         'gpu/chrome_content_gpu_client.cc',
         'gpu/chrome_content_gpu_client.h',
       ],
       'dependencies': [
         '../content/content.gyp:content_common',
         '../content/content.gyp:content_gpu',
       ],
       'conditions': [
         ['chromeos==1', {
           'dependencies': [
             '../components/components.gyp:arc_mojo_bindings',
           ],
           'sources': [
+            'gpu/arc_gpu_video_decode_accelerator.cc',
+            'gpu/arc_gpu_video_decode_accelerator.h',
             'gpu/arc_video_accelerator.h',
             'gpu/gpu_arc_video_service.cc',
             'gpu/gpu_arc_video_service.h',
           ],
         }],
       ],
     },
   ],
 }