Refators display related functionality into own class

components/mus/ws/test_server_window_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 COMPONENTS_MUS_WS_TEST_SERVER_WINDOW_DELEGATE_H_
 #define COMPONENTS_MUS_WS_TEST_SERVER_WINDOW_DELEGATE_H_
 
 #include "base/macros.h"
 #include "components/mus/ws/server_window_delegate.h"
 
 namespace mus {
 
 namespace ws {
 
 struct WindowId;
 
 class TestServerWindowDelegate : public ServerWindowDelegate {
  public:
   TestServerWindowDelegate();
   ~TestServerWindowDelegate() override;
 
   void set_root_window(const ServerWindow* window) { root_window_ = window; }
 
  private:
   // ServerWindowDelegate:
   mus::SurfacesState* GetSurfacesState() override;
-  void OnScheduleWindowPaint(const ServerWindow* window) override;
+  void OnScheduleWindowPaint(ServerWindow* window) override;
   const ServerWindow* GetRootWindow(const ServerWindow* window) const override;
   void ScheduleSurfaceDestruction(ServerWindow* window) override;
   ServerWindow* FindWindowForSurface(
       const ServerWindow* ancestor,
       mojom::SurfaceType surface_type,
       const ClientWindowId& client_window_id) override;
 
   const ServerWindow* root_window_;
 
   DISALLOW_COPY_AND_ASSIGN(TestServerWindowDelegate);
 };
 
 }  // namespace ws
 
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_WS_TEST_SERVER_WINDOW_DELEGATE_H_