Cleanup display creation in mus tests.

services/ui/ws/window_tree_unittest.cc

Index: services/ui/ws/window_tree_unittest.cc
diff --git a/services/ui/ws/window_tree_unittest.cc b/services/ui/ws/window_tree_unittest.cc
index 6e0d53ae73e8b47ff54f64bfc3e97a149f9cc9ef..10c6cbb382fb5ad1283264d98d4634d3ea531b5d 100644
--- a/services/ui/ws/window_tree_unittest.cc
+++ b/services/ui/ws/window_tree_unittest.cc
@@ -18,6 +18,7 @@
 #include "services/ui/public/interfaces/window_tree.mojom.h"
 #include "services/ui/surfaces/display_compositor.h"
 #include "services/ui/ws/default_access_policy.h"
+#include "services/ui/ws/display_manager.h"
 #include "services/ui/ws/ids.h"
 #include "services/ui/ws/platform_display.h"
 #include "services/ui/ws/platform_display_factory.h"
@@ -1355,9 +1356,10 @@ TEST_F(WindowTreeShutdownTest, DontSendMessagesDuringShutdown) {
     // Create a tree with one window.
     WindowServerTestHelper ws_test_helper;
     WindowServer* window_server = ws_test_helper.window_server();
+    TestPlatformScreen platform_screen;
+    platform_screen.Init(window_server->display_manager());
     window_server->user_id_tracker()->AddUserId(kTestUserId1);
-    const int kNumHostsToCreate = 1;
-    ws_test_helper.window_server_delegate()->CreateDisplays(kNumHostsToCreate);
+    platform_screen.AddDisplay();
 
     AddWindowManager(window_server, kTestUserId1);
     window_server->user_id_tracker()->SetActiveUserId(kTestUserId1);