Only send the FrameSinkId to client when it is necessary

ui/aura/test/mus/window_tree_client_private.cc

Index: ui/aura/test/mus/window_tree_client_private.cc
diff --git a/ui/aura/test/mus/window_tree_client_private.cc b/ui/aura/test/mus/window_tree_client_private.cc
index 89bd828c878aec6166bd24066eb74a4edd70e04a..3518bd39e19243bf3cdea2820d909ec7404deced 100644
--- a/ui/aura/test/mus/window_tree_client_private.cc
+++ b/ui/aura/test/mus/window_tree_client_private.cc
@@ -31,7 +31,7 @@ void WindowTreeClientPrivate::OnEmbed(ui::mojom::WindowTree* window_tree) {
   const Id focused_window_id = 0;
   tree_client_impl_->OnEmbedImpl(window_tree, 1, std::move(root_data),
                                  display_id, focused_window_id, true,
-                                 cc::FrameSinkId(1, 1), base::nullopt);
+                                 base::nullopt);
 }
 
 WindowTreeHostMus* WindowTreeClientPrivate::CallWmNewDisplayAdded(
@@ -49,9 +49,8 @@ WindowTreeHostMus* WindowTreeClientPrivate::CallWmNewDisplayAdded(
     const display::Display& display,
     ui::mojom::WindowDataPtr root_data,
     bool parent_drawn) {
-  return tree_client_impl_->WmNewDisplayAddedImpl(
-      display, std::move(root_data), parent_drawn, cc::FrameSinkId(1, 1),
-      base::nullopt);
+  return tree_client_impl_->WmNewDisplayAddedImpl(display, std::move(root_data),
+                                                  parent_drawn, base::nullopt);
 }
 
 void WindowTreeClientPrivate::CallOnWindowInputEvent(