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

ui/gl/gl.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': {
     'chromium_code': 1,
   },
 
   'targets': [
@@ skipping 22 matching lines @@
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '<(gl_binding_output_dir)',
         ],
       },
       'export_dependent_settings': [
         '<(DEPTH)/third_party/mesa/mesa.gyp:mesa_headers',
       ],
      'sources': [
+        'async_pixel_transfer_delegate.h',
+        'async_pixel_transfer_delegate_stub.cc',
+        'async_pixel_transfer_delegate_stub.h',
         'gl_bindings.h',
         'gl_bindings_skia_in_process.cc',
         'gl_bindings_skia_in_process.h',
         'gl_context.cc',
         'gl_context.h',
         'gl_context_android.cc',
         'gl_context_linux.cc',
         'gl_context_mac.mm',
         'gl_context_osmesa.cc',
         'gl_context_osmesa.h',
@@ skipping 222 matching lines @@
         ],
       },
       'sources': [
         'gl_mock.h',
         'gl_mock.cc',
         '<(gl_binding_output_dir)/gl_mock_autogen_gl.h',
       ],
     },
   ],
 }