mus: Changes SetDisplayRoot() to create actual display

services/ui/display/screen_manager_stub_internal.h

 // Copyright 2016 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_DISPLAY_SCREEN_MANAGER_STUB_INTERNAL_H_
 #define SERVICES_UI_DISPLAY_SCREEN_MANAGER_STUB_INTERNAL_H_
 
 #include <stdint.h>
 
 #include "base/memory/weak_ptr.h"
 #include "services/ui/display/screen_manager.h"
 #include "ui/display/display.h"
 
 namespace display {
 
+class ScreenBase;
+
 // ScreenManagerStubInternal provides the necessary functionality to configure a
 // fixed 1024x768 display for non-ozone platforms.
 class ScreenManagerStubInternal : public ScreenManager {
  public:
   ScreenManagerStubInternal();
   ~ScreenManagerStubInternal() override;
 
  private:
   // Fake creation of a single 1024x768 display.
   void FixedSizeScreenConfiguration();
 
   // ScreenManager.
   void AddInterfaces(service_manager::BinderRegistry* registry) override;
   void Init(ScreenManagerDelegate* delegate) override;
   void RequestCloseDisplay(int64_t display_id) override;
+  display::ScreenBase* GetScreen() override;
 
   // Sample display information.
   Display display_;
 
   ScreenManagerDelegate* delegate_ = nullptr;
 
+  std::unique_ptr<ScreenBase> screen_;
+
   base::WeakPtrFactory<ScreenManagerStubInternal> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenManagerStubInternal);
 };
 
 }  // namespace display
 
 #endif  // SERVICES_UI_DISPLAY_SCREEN_MANAGER_STUB_INTERNAL_H_