mus: Changes SetDisplayRoot() to create actual display

services/ui/ws/window_server_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 SERVICES_UI_WS_WINDOW_SERVER_DELEGATE_H_
 #define SERVICES_UI_WS_WINDOW_SERVER_DELEGATE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 35 matching lines @@
 
   // Creates a WindowTreeBinding. Default implementation returns null, which
   // creates DefaultBinding.
   virtual std::unique_ptr<WindowTreeBinding> CreateWindowTreeBinding(
       BindingType type,
       ws::WindowServer* window_server,
       ws::WindowTree* tree,
       mojom::WindowTreeRequest* tree_request,
       mojom::WindowTreeClientPtr* client);
 
+  // Called prior to a new WindowTree being created for a
+  // WindowManagerWindowTreeFactory. |automatically_create_display_roots|
+  // mirrors that of CreateWindowTree(). See it for details.
+  virtual void OnWillCreateTreeForWindowManager(
+      bool automatically_create_display_roots);
+
  protected:
   virtual ~WindowServerDelegate() {}
 };
 
 }  // namespace ws
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_WINDOW_SERVER_DELEGATE_H_