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

gpu/command_buffer/service/gles2_cmd_decoder_mock.h

Index: gpu/command_buffer/service/gles2_cmd_decoder_mock.h
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder_mock.h b/gpu/command_buffer/service/gles2_cmd_decoder_mock.h
index 427c44eab3c9e0f869ce4bcbb699c7e9d2a18c75..e92ca940c944af00b401674bc1998e249cf455d0 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder_mock.h
+++ b/gpu/command_buffer/service/gles2_cmd_decoder_mock.h
@@ -57,6 +57,10 @@ class MockGLES2Decoder : public GLES2Decoder {
   MOCK_METHOD0(GetVertexArrayManager, gpu::gles2::VertexArrayManager*());
   MOCK_METHOD1(SetResizeCallback, void(const base::Callback<void(gfx::Size)>&));
   MOCK_METHOD1(SetStreamTextureManager, void(StreamTextureManager*));
+  MOCK_METHOD0(GetAsyncPixelTransferDelegate,
+      gfx::AsyncPixelTransferDelegate*());
+  MOCK_METHOD1(SetAsyncPixelTransferDelegate,
+      void(gfx::AsyncPixelTransferDelegate*));
   MOCK_METHOD3(DoCommand, error::Error(unsigned int command,
                                        unsigned int arg_count,
                                        const void* cmd_data));