cc: Setup API to release OutputSurface from LTHClient.

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 4d72eb246854c54d69d5c89b806c73be7d989a0b..c09550fb7999d1f0166cd9f1b10a6ad609acdda7 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -397,6 +397,11 @@ void LayerTreeHost::SetOutputSurface(scoped_ptr<OutputSurface> surface) {
   proxy_->SetOutputSurface(surface.Pass());
 }
 
+scoped_ptr<OutputSurface> LayerTreeHost::GetOutputSurface() {
+  output_surface_lost_ = true;
+  return proxy_->GetOutputSurface();
+}
+
 void LayerTreeHost::RequestNewOutputSurface() {
   client_->RequestNewOutputSurface();
 }