Allow parallel creation of windows

services/ui/demo/mus_demo_external.h

Index: services/ui/demo/mus_demo_external.h
diff --git a/services/ui/demo/mus_demo_external.h b/services/ui/demo/mus_demo_external.h
index 844e04186fd225084c1cbcd2cf7c175ce6de503c..9fb1d3f098a1a33d8cf7a6e884e0bbcfba0fa9b0 100644
--- a/services/ui/demo/mus_demo_external.h
+++ b/services/ui/demo/mus_demo_external.h
@@ -29,13 +29,16 @@ class MusDemoExternal : public MusDemo {
   std::unique_ptr<aura::WindowTreeClient> CreateWindowTreeClient() final;
 
   // aura::WindowTreeClientDelegate:
-  void OnEmbed(std::unique_ptr<aura::WindowTreeHostMus> window_tree_host) final;
+  void OnRootWindowEmbed(aura::WindowTreeHostMus* window_tree_host) final;

[fwang, 2017/03/15 14:37:56]

What about OnEmbedRootReady, to be consistent with OnEmbedRootDestroyed?

I guess the OnEmbed in the parent class should be final.

[msisov, 2017/03/16 08:17:52]

Done.

   void OnEmbedRootDestroyed(aura::WindowTreeHostMus* window_tree_host) final;
 
   size_t initialized_windows_count_ = 0;
 
   size_t number_of_windows_ = 1;
 
+  std::vector<std::unique_ptr<aura::WindowTreeHostMus>>
+      window_tree_host_mus_list_;

[fwang, 2017/03/15 14:37:56]

I think you can just keep this in WindowTreeData.

[msisov, 2017/03/16 08:17:52]

Done.

+
   DISALLOW_COPY_AND_ASSIGN(MusDemoExternal);
 };