Add PlatformScreenDelegate and start implementation.

services/ui/ws/test_utils.cc

Index: services/ui/ws/test_utils.cc
diff --git a/services/ui/ws/test_utils.cc b/services/ui/ws/test_utils.cc
index b9ef94cf25b48b22c0dfabc569c912e1866f6735..9e1c7c0b1b4889a483e15107399012a3a24c415d 100644
--- a/services/ui/ws/test_utils.cc
+++ b/services/ui/ws/test_utils.cc
@@ -426,8 +426,7 @@ WindowEventTargetingHelper::WindowEventTargetingHelper()
       surfaces_state_(new SurfacesState()),
       window_server_(nullptr) {
   PlatformDisplay::set_factory_for_testing(&platform_display_factory_);
-  window_server_.reset(
-      new WindowServer(&window_server_delegate_, surfaces_state_));
+  window_server_.reset(new WindowServer(&window_server_delegate_));
   PlatformDisplayInitParams display_init_params;
   display_init_params.surfaces_state = surfaces_state_;
   display_ = new Display(window_server_.get(), display_init_params);