Have PlatformScreen use DisplayConfigurator.

services/ui/ws/platform_screen.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_WS_PLATFORM_SCREEN_H_
 #define SERVICES_UI_WS_PLATFORM_SCREEN_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
 
 namespace gfx {
 class Rect;
 }
 
 namespace ui {
 namespace ws {
 
 // PlatformScreen provides the necessary functionality to configure all
 // attached physical displays.
 class PlatformScreen {
  public:
+  using ConfiguredDisplayCallback =
+      base::Callback<void(int64_t, const gfx::Rect&)>;
+
   virtual ~PlatformScreen() {}
 
   // Creates a PlatformScreen instance.
   static std::unique_ptr<PlatformScreen> Create();
 
   // Initializes platform specific screen resources.
   virtual void Init() = 0;
 
-  using ConfiguredDisplayCallback =
-      base::Callback<void(int64_t, const gfx::Rect&)>;
-
   // ConfigurePhysicalDisplay() configures a single physical display and returns
   // its id and bounds for it via |callback|.
   virtual void ConfigurePhysicalDisplay(
       const ConfiguredDisplayCallback& callback) = 0;
 };
 
 }  // namespace ws
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_PLATFORM_SCREEN_H_