Allow parallel creation of windows

ui/aura/mus/window_tree_client_delegate.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_AURA_MUS_WINDOW_TREE_CLIENT_DELEGATE_H_
 #define UI_AURA_MUS_WINDOW_TREE_CLIENT_DELEGATE_H_
 
 #include <memory>
 #include <string>
 
 #include "services/service_manager/public/interfaces/interface_provider.mojom.h"
 #include "services/ui/public/interfaces/window_tree.mojom.h"
 #include "ui/aura/aura_export.h"
 
 namespace aura {
 
 class PropertyConverter;
 class Window;
 class WindowTreeClient;
 class WindowTreeHostMus;
 
 // Interface implemented by an application using mus.
 class AURA_EXPORT WindowTreeClientDelegate {
  public:
   // Called when the application implementing this interface is embedded.
   // NOTE: this is only invoked if the WindowTreeClient is created with an
   // InterfaceRequest.
   virtual void OnEmbed(std::unique_ptr<WindowTreeHostMus> window_tree_host) = 0;
 
+  // Called when the application implementing this interface is embedded and
+  // uses external window mode.
+  virtual void OnEmbedRootReady(WindowTreeHostMus* window_tree_host);
+
   // Sent when another app is embedded in |root| (one of the roots of the
   // connection). Afer this call |root| is deleted. If the associated
   // WindowTreeClient was created from a WindowTreeClientRequest then
   // OnEmbedRootDestroyed() is called after the window is deleted.
   virtual void OnUnembed(Window* root);
 
   // Called when the embed root has been destroyed on the server side (or
   // another client was embedded in the same window). This is called in two
   // distinct cases:
   // . If the WindowTreeClient was created from an InterfaceRequest. In this
@@ skipping 20 matching lines @@
 
   virtual PropertyConverter* GetPropertyConverter() = 0;
 
  protected:
   virtual ~WindowTreeClientDelegate() {}
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_TREE_CLIENT_DELEGATE_H_