WIP: Propagate SurfaceID up window tree hierarchy

ash/mus/root_window_controller.cc

Index: ash/mus/root_window_controller.cc
diff --git a/ash/mus/root_window_controller.cc b/ash/mus/root_window_controller.cc
index c0ebce22f45a09aec54082ba165ba7a090786c10..3fc8b15acf3defd7e1c5b388b330034168df17a6 100644
--- a/ash/mus/root_window_controller.cc
+++ b/ash/mus/root_window_controller.cc
@@ -61,6 +61,7 @@ RootWindowController::RootWindowController(WindowManager* window_manager,
   wm_root_window_controller_->CreateLayoutManagers();
   CreateLayoutManagers();
 
+  root_->SetIsContainer();
   disconnected_app_handler_.reset(new DisconnectedAppHandler(root));
 
   // Force a layout of the root, and its children, RootWindowLayout handles
@@ -100,6 +101,7 @@ ui::Window* RootWindowController::NewTopLevelWindow(
   // TODO(sky): constrain and validate properties before passing to server.
   ui::Window* window = root_->window_tree()->NewWindow(properties);
   window->SetBounds(CalculateDefaultBounds(window));
+  // window->SetIsContainer();
 
   ui::Window* container_window = nullptr;
   mojom::Container container;
@@ -110,6 +112,7 @@ ui::Window* RootWindowController::NewTopLevelWindow(
     container_window = WmWindowMus::GetMusWindow(wm::GetDefaultParent(
         WmWindowMus::Get(root_), WmWindowMus::Get(window), window->bounds()));
   }
+  container_window->SetIsContainer();
   DCHECK(WmWindowMus::Get(container_window)->IsContainer());
 
   if (provide_non_client_frame) {