mus: Changes SetDisplayRoot() to create actual display

services/ui/display/screen_manager_ozone_external.cc

 // Copyright 2017 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.
 
 #include "services/ui/display/screen_manager_ozone_external.h"
 
 #include <memory>
 
 #include "services/service_manager/public/cpp/binder_registry.h"
+#include "ui/display/screen_base.h"
 #include "ui/display/types/display_constants.h"
 
 namespace display {
 
 // static
 std::unique_ptr<ScreenManager> ScreenManager::Create() {
   return base::MakeUnique<ScreenManagerOzoneExternal>();
 }
 
-ScreenManagerOzoneExternal::ScreenManagerOzoneExternal() {}
+ScreenManagerOzoneExternal::ScreenManagerOzoneExternal()
+    : screen_(base::MakeUnique<display::ScreenBase>()) {}
 
 ScreenManagerOzoneExternal::~ScreenManagerOzoneExternal() {}
 
 void ScreenManagerOzoneExternal::AddInterfaces(
     service_manager::BinderRegistry* registry) {}
 
 void ScreenManagerOzoneExternal::Init(ScreenManagerDelegate* delegate) {}
 
 void ScreenManagerOzoneExternal::RequestCloseDisplay(int64_t display_id) {}
 
+display::ScreenBase* ScreenManagerOzoneExternal::GetScreen() {
+  return screen_.get();
+}
+
 }  // namespace display