Allow parallel creation of windows

services/ui/demo/mus_demo.h

Index: services/ui/demo/mus_demo.h
diff --git a/services/ui/demo/mus_demo.h b/services/ui/demo/mus_demo.h
index 251a505818c42e56c559e517e5f1437bc7e9895c..4f6910b79b9fb2bd80b75cf22378c6e6f6115899 100644
--- a/services/ui/demo/mus_demo.h
+++ b/services/ui/demo/mus_demo.h
@@ -46,17 +46,24 @@ class MusDemo : public service_manager::Service,
   void AddPrimaryDisplay(const display::Display& display);
 
   // These functions help to manage the list of WindowTreeData structures.
-  // AppendWindowTreeData is used to add an uninitialized structure at the end
+  // AppendWindowTreeData is used to add uninitialized structures at the end
   // of the list. When a new WindowTreeHostMus is created and is sent to
-  // MusDemo (via OnWmNewDisplay or OnEmbed), the WindowTreeData is initialized
-  // by a call to InitWindowTreeData and the demo starts. When the destruction
-  // of the WindowTreeHostMus is announced to MusDemo (via OnWmDisplayRemoved
-  // or OnEmbedRootDestroyed), the corresponding WindowTreeData is removed by
-  // a call to RemoveWindowTreeData.
+  // MusDemo via OnWmNewDisplay, the WindowTreeData is initialized
+  // by a call to InitWindowTreeData and the demo starts. In case if
+  // OnEmbedRootReady is called, corresponding WindowTreeData is found by
+  // looking associated WindowTreeHostMus with it. When the destruction of the
+  // WindowTreeHostMus is announced to MusDemo (via OnWmDisplayRemoved or
+  // OnEmbedRootDestroyed), the corresponding WindowTreeData is removed by a
+  // call to RemoveWindowTreeData.
   void AppendWindowTreeData(std::unique_ptr<WindowTreeData> window_tree_data);
   void InitWindowTreeData(
       std::unique_ptr<aura::WindowTreeHostMus> window_tree_host);
+  // Is called in case if OnEmbedRootReady is called. Uses WindowTreeHostMus*
+  // to find an associated WindowTreeData with it.
+  void InitWindowTreeDataExternal(aura::WindowTreeHostMus* window_tree_host);

[fwang, 2017/03/16 08:59:48]

I would make HasPendingWindowTreeData protected and move this function specific
to "external mode" into the MusDemoExternal derived class. But actually, I think
we no longer really need HasPendingWindowTreeData, now that the last element is
no longer the pending child and use FindWindowTreeData instead.

[msisov(use msisov igalia.com), 2017/03/16 09:21:32]

Agree, HasPendingWindowTreeData is not longer needed. We just check that
WindowTreeData is not initialized when Init() is called and that
InitWindowTreeData

   void RemoveWindowTreeData(aura::WindowTreeHostMus* window_tree_host);
+  std::vector<std::unique_ptr<WindowTreeData>>::iterator FindWindowTreeData(
+      aura::WindowTreeHostMus* window_tree_host);
 
   aura::WindowTreeClient* window_tree_client() {
     return window_tree_client_.get();