Add PlatformScreenDelegate and start implementation.

services/ui/ws/window_tree_host_factory.h

Index: services/ui/ws/window_tree_host_factory.h
diff --git a/services/ui/ws/window_tree_host_factory.h b/services/ui/ws/window_tree_host_factory.h
index 367f8646d9b2d7bbdbff496acefcbb22d4f4a0df..0fa3d514e6935dc884864eaa9f070cb5d7a71e2c 100644
--- a/services/ui/ws/window_tree_host_factory.h
+++ b/services/ui/ws/window_tree_host_factory.h
@@ -19,10 +19,7 @@ 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);
@@ -34,7 +31,7 @@ class WindowTreeHostFactory : public mojom::WindowTreeHostFactory {
 
   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);