gpu: Implement idle async pixel transfers.

ui/gl/async_pixel_transfer_delegate.h

Index: ui/gl/async_pixel_transfer_delegate.h
diff --git a/ui/gl/async_pixel_transfer_delegate.h b/ui/gl/async_pixel_transfer_delegate.h
index e2d1d6c89951b01353c339d73fd7b5f9140067d1..aa66dc467959c0fb087dd5c6227eb1dd4b57109f 100644
--- a/ui/gl/async_pixel_transfer_delegate.h
+++ b/ui/gl/async_pixel_transfer_delegate.h
@@ -113,6 +113,9 @@ class GL_EXPORT AsyncPixelTransferDelegate {
   virtual uint32 GetTextureUploadCount() = 0;
   virtual base::TimeDelta GetTotalTextureUploadTime() = 0;
 
+  virtual void ProcessPendingTransfers() = 0;

[Sami, 2013/03/07 16:57:19]

Can we name these somehow so that the distinction between off- and on-thread
transfers is clear? I think having the Android delegate always return false from
a function called HasPendingTransfers seems weird.

ProcessPendingIdleTransfers maybe? At least let's put a comment here.

[reveman, 2013/03/07 20:21:04]

I agree.
I renamed HasPendingTransfers() to CanProcessPendingTransfers() and added a
comment that explains what these functions are for.

+  virtual bool HasPendingTransfers() = 0;
+
  protected:
   AsyncPixelTransferDelegate() {}
   // For testing, as returning scoped_ptr wouldn't work with MOCK_METHOD.