Use null rather than empty frame to lock Surface resources

cc/surfaces/surface_display_output_surface.cc

Index: cc/surfaces/surface_display_output_surface.cc
diff --git a/cc/surfaces/surface_display_output_surface.cc b/cc/surfaces/surface_display_output_surface.cc
index 42f828f55b3a39610002a28010a533f6bcae9a3d..ece25711a0ed563de34e57f7c3d2426e132b7070 100644
--- a/cc/surfaces/surface_display_output_surface.cc
+++ b/cc/surfaces/surface_display_output_surface.cc
@@ -80,12 +80,8 @@ bool SurfaceDisplayOutputSurface::BindToClient(OutputSurfaceClient* client) {
 }
 
 void SurfaceDisplayOutputSurface::ForceReclaimResources() {
-  if (!surface_id_.is_null()) {
-    scoped_ptr<CompositorFrame> empty_frame(new CompositorFrame());
-    empty_frame->delegated_frame_data.reset(new DelegatedFrameData);
-    factory_.SubmitFrame(surface_id_, empty_frame.Pass(),
-                         SurfaceFactory::DrawCallback());
-  }
+  if (!surface_id_.is_null())
+    factory_.SubmitFrame(surface_id_, nullptr, SurfaceFactory::DrawCallback());
 }
 
 void SurfaceDisplayOutputSurface::ReturnResources(