Mus Demo: Refactor code to prepare multiple windows in external mode

services/ui/demo/mus_demo_internal.h

Index: services/ui/demo/mus_demo_internal.h
diff --git a/services/ui/demo/mus_demo_internal.h b/services/ui/demo/mus_demo_internal.h
index 3a72654b90a1300a402598ae496c2de35fc95445..ee93d5e38840d8e148e4fa14aa908b14b0e58451 100644
--- a/services/ui/demo/mus_demo_internal.h
+++ b/services/ui/demo/mus_demo_internal.h
@@ -27,8 +27,8 @@ class MusDemoInternal : public MusDemo, public aura::WindowManagerDelegate {
 
  private:
   // ui::demo::MusDemo:
-  void OnStartImpl(std::unique_ptr<aura::WindowTreeClient>* window_tree_client,
-                   std::unique_ptr<WindowTreeData>* window_tree_data) final;
+  void OnStartImpl() final;
+  std::unique_ptr<aura::WindowTreeClient> CreateWindowTreeClient() final;
 
   // aura::WindowManagerDelegate:
   void SetWindowManagerClient(aura::WindowManagerClient* client) final;