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..4efc5741d22d74d5152c0e63707d399717bf5a0f 100644
--- a/ui/gl/async_pixel_transfer_delegate.h
+++ b/ui/gl/async_pixel_transfer_delegate.h
@@ -113,6 +113,14 @@ class GL_EXPORT AsyncPixelTransferDelegate {
   virtual uint32 GetTextureUploadCount() = 0;
   virtual base::TimeDelta GetTotalTextureUploadTime() = 0;
 
+  // ProcessPendingTransfers() will be called at a good time
+  // to process a small amount of pending transfer work while
+  // CanProcessPendingTransfers() returns true. Implementations
+  // that can't dispatch work to separate threads should use
+  // this to avoid blocking the caller thread inappropriately.
+  virtual void ProcessPendingTransfers() = 0;
+  virtual bool CanProcessPendingTransfers() = 0;
+
  protected:
   AsyncPixelTransferDelegate() {}
   // For testing, as returning scoped_ptr wouldn't work with MOCK_METHOD.