gpu: Add async pixel transfer interface, stub and tests.

gpu/gpu.gyp

 # 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.
 
 {
   'variables': {
     'nacl_win64_target': 0,
   },
   'includes': [
     'gpu_common.gypi',
@@ skipping 137 matching lines @@
         'command_buffer/common/command_buffer_mock.cc',
         'command_buffer/common/command_buffer_mock.h',
         'command_buffer/common/command_buffer_shared_test.cc',
         'command_buffer/common/debug_marker_manager_unittest.cc',
         'command_buffer/common/gles2_cmd_format_test.cc',
         'command_buffer/common/gles2_cmd_format_test_autogen.h',
         'command_buffer/common/gles2_cmd_utils_unittest.cc',
         'command_buffer/common/id_allocator_test.cc',
         'command_buffer/common/trace_event.h',
         'command_buffer/common/unittest_main.cc',
+        'command_buffer/service/async_pixel_transfer_delegate_mock.h',
+        'command_buffer/service/async_pixel_transfer_delegate_mock.cc',
         'command_buffer/service/buffer_manager_unittest.cc',
         'command_buffer/service/cmd_parser_test.cc',
         'command_buffer/service/command_buffer_service_unittest.cc',
         'command_buffer/service/common_decoder_unittest.cc',
         'command_buffer/service/context_group_unittest.cc',
         'command_buffer/service/feature_info_unittest.cc',
         'command_buffer/service/framebuffer_manager_unittest.cc',
         'command_buffer/service/gles2_cmd_decoder_unittest.cc',
         'command_buffer/service/gles2_cmd_decoder_unittest_0_autogen.h',
         'command_buffer/service/gles2_cmd_decoder_unittest_1.cc',
@@ skipping 257 matching lines @@
           'configurations': {
             'Common_Base': {
               'msvs_target_platform': 'x64',
             },
           },
         },
       ],
     }],
   ],
 }