mus: Changes SetDisplayRoot() to create actual display

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 50cbcd2791604c94c27aebfd915f2867dfec0dff..dea186977293440ec574a900497b3e1bc952f8d7 100644
--- a/services/ui/ws/test_utils.cc
+++ b/services/ui/ws/test_utils.cc
@@ -142,6 +142,10 @@ void TestScreenManager::Init(display::ScreenManagerDelegate* delegate) {
   display::Screen::SetScreenInstance(screen_.get());
 }
 
+display::ScreenBase* TestScreenManager::GetScreen() {
+  return screen_.get();
+}
+
 // TestPlatformDisplayFactory  -------------------------------------------------
 
 TestPlatformDisplayFactory::TestPlatformDisplayFactory(