mustash: enable GPU Compositing in renderer

content/renderer/render_widget_window_tree_client_factory.cc

Index: content/renderer/render_widget_window_tree_client_factory.cc
diff --git a/content/renderer/render_widget_window_tree_client_factory.cc b/content/renderer/render_widget_window_tree_client_factory.cc
index fefec083d13126005439e6f16728db49a70e516a..ac158bcd1f7f085ab82c7bbcf38d59e1224b1ffb 100644
--- a/content/renderer/render_widget_window_tree_client_factory.cc
+++ b/content/renderer/render_widget_window_tree_client_factory.cc
@@ -51,8 +51,10 @@ class RenderWidgetWindowTreeClientFactoryImpl
   // mojom::RenderWidgetWindowTreeClientFactory implementation.
   void CreateWindowTreeClientForRenderWidget(
       uint32_t routing_id,
-      mojo::InterfaceRequest<mus::mojom::WindowTreeClient> request) override {
+      mojo::InterfaceRequest<mus::mojom::WindowTreeClient> request,
+      const CreateWindowTreeClientForRenderWidgetCallback& callback) override {
     new RenderWidgetMusConnection(routing_id, request.Pass());
+    callback.Run(true);
   }
 
   mojo::WeakBindingSet<mojom::RenderWidgetWindowTreeClientFactory> bindings_;