gpu: Add the ability to wait on upload completion.

ui/gl/async_pixel_transfer_delegate_stub.cc

Index: ui/gl/async_pixel_transfer_delegate_stub.cc
diff --git a/ui/gl/async_pixel_transfer_delegate_stub.cc b/ui/gl/async_pixel_transfer_delegate_stub.cc
index b4f36396cbe954896deda8c0bf8addc1c4bd8786..093cb116b28e3a3247861c0be2d3b9e27e1c83e3 100644
--- a/ui/gl/async_pixel_transfer_delegate_stub.cc
+++ b/ui/gl/async_pixel_transfer_delegate_stub.cc
@@ -139,6 +139,11 @@ void AsyncPixelTransferDelegateStub::AsyncTexSubImage2D(
   total_texture_upload_time_ += base::TimeTicks::HighResNow() - begin_time;
 }
 
+void AsyncPixelTransferDelegateStub::WaitForTransferCompletion(
+    AsyncPixelTransferState* state) {
+  // Already done.
+}
+
 uint32 AsyncPixelTransferDelegateStub::GetTextureUploadCount() {
   return texture_upload_count_;
 }