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

gpu/command_buffer/service/gles2_cmd_decoder.h

Index: gpu/command_buffer/service/gles2_cmd_decoder.h
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.h b/gpu/command_buffer/service/gles2_cmd_decoder.h
index 9b089e32e2bbaefc0d62d7f97d2b90d161b11776..43111985786448ca9b82a10c977c762d6cd0caf8 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.h
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.h
@@ -20,6 +20,7 @@
 namespace gfx {
 class GLContext;
 class GLSurface;
+class AsyncPixelTransferDelegate;
 }
 
 namespace gpu {
@@ -157,6 +158,11 @@ class GPU_EXPORT GLES2Decoder : public base::SupportsWeakPtr<GLES2Decoder>,
 
   virtual void SetStreamTextureManager(StreamTextureManager* manager) = 0;
 
+  // Interface to performing async pixel transfers.
+  virtual gfx::AsyncPixelTransferDelegate* GetAsyncPixelTransferDelegate() = 0;
+  virtual void SetAsyncPixelTransferDelegate(
+      gfx::AsyncPixelTransferDelegate* delegate) = 0;
+
   // Get the service texture ID corresponding to a client texture ID.
   // If no such record is found then return false.
   virtual bool GetServiceTextureId(uint32 client_texture_id,