Add PlatformScreenDelegate and start implementation.

services/ui/ws/window_tree_host_factory.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_WINDOW_TREE_HOST_FACTORY_H_
 #define SERVICES_UI_WS_WINDOW_TREE_HOST_FACTORY_H_
 
 #include <stdint.h>
 
 #include "mojo/public/cpp/bindings/binding_set.h"
 #include "services/ui/public/interfaces/window_tree_host.mojom.h"
 #include "services/ui/ws/platform_display_init_params.h"
 #include "services/ui/ws/user_id.h"
 
 namespace ui {
 namespace ws {
 
 class WindowServer;
 
 class WindowTreeHostFactory : public mojom::WindowTreeHostFactory {
  public:
-  WindowTreeHostFactory(
-      WindowServer* window_server,
-      const UserId& user_id,
-      const PlatformDisplayInitParams& platform_display_init_params);
+  WindowTreeHostFactory(WindowServer* window_server, const UserId& user_id);
   ~WindowTreeHostFactory() override;
 
   void AddBinding(mojom::WindowTreeHostFactoryRequest request);
 
  private:
   // mojom::WindowTreeHostFactory implementation.
   void CreateWindowTreeHost(mojom::WindowTreeHostRequest host,
                             mojom::WindowTreeClientPtr tree_client) override;
 
   WindowServer* window_server_;
   const UserId user_id_;
-  const PlatformDisplayInitParams platform_display_init_params_;
+  PlatformDisplayInitParams platform_display_init_params_;
   mojo::BindingSet<mojom::WindowTreeHostFactory> bindings_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeHostFactory);
 };
 
 }  // namespace ws
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_WINDOW_TREE_HOST_FACTORY_H_