Cleanup display creation in mus tests.

services/ui/ws/window_manager_state_unittest.cc

Index: services/ui/ws/window_manager_state_unittest.cc
diff --git a/services/ui/ws/window_manager_state_unittest.cc b/services/ui/ws/window_manager_state_unittest.cc
index fd3c5a286807c7ba1e2668229d254dc8f092f435..e14a70f82159fd47599f687d65a2866fa1c3d05d 100644
--- a/services/ui/ws/window_manager_state_unittest.cc
+++ b/services/ui/ws/window_manager_state_unittest.cc
@@ -547,8 +547,10 @@ TEST_F(WindowManagerStateTest, PostAcceleratorForgotten) {
 // with no roots.
 TEST(WindowManagerStateShutdownTest, DestroyTreeBeforeDisplay) {
   WindowServerTestHelper ws_test_helper;
-  ws_test_helper.window_server_delegate()->CreateDisplays(1);
   WindowServer* window_server = ws_test_helper.window_server();
+  TestPlatformScreen platform_screen;
+  platform_screen.Init(window_server->display_manager());
+  platform_screen.AddDisplay();
   const UserId kUserId1 = "2";
   AddWindowManager(window_server, kUserId1);
   ASSERT_EQ(1u, window_server->display_manager()->displays().size());