chromeos: fix focus for mushrome

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 11d475986d844558be8146668afe17e87c84e70c..89bd828c878aec6166bd24066eb74a4edd70e04a 100644
--- a/ui/aura/test/mus/window_tree_client_private.cc
+++ b/ui/aura/test/mus/window_tree_client_private.cc
@@ -99,6 +99,11 @@ void WindowTreeClientPrivate::SetTreeAndClientId(
   tree_client_impl_->client_id_ = client_id;
 }
 
+void WindowTreeClientPrivate::SetWindowManagerClient(
+    ui::mojom::WindowManagerClient* client) {
+  tree_client_impl_->window_manager_client_ = client;
+}
+
 bool WindowTreeClientPrivate::HasPointerWatcher() {
   return tree_client_impl_->has_pointer_watcher_;
 }