Cleanup display creation in mus tests.

services/ui/ws/cursor_unittest.cc

Index: services/ui/ws/cursor_unittest.cc
diff --git a/services/ui/ws/cursor_unittest.cc b/services/ui/ws/cursor_unittest.cc
index a3f59444200db61faa16f4b44407e36940807fdc..fa27a94a8ed7cc059ab98523af908ddd07943a03 100644
--- a/services/ui/ws/cursor_unittest.cc
+++ b/services/ui/ws/cursor_unittest.cc
@@ -49,7 +49,8 @@ class CursorTest : public testing::Test {
  protected:
   // testing::Test:
   void SetUp() override {
-    window_server_delegate()->CreateDisplays(1);
+    platform_screen_.Init(window_server()->display_manager());
+    platform_screen_.AddDisplay();
 
     // As a side effect, this allocates Displays.
     AddWindowManager(window_server(), kTestId1);
@@ -103,6 +104,7 @@ class CursorTest : public testing::Test {
 
  private:
   WindowServerTestHelper ws_test_helper_;
+  TestPlatformScreen platform_screen_;
   DISALLOW_COPY_AND_ASSIGN(CursorTest);
 };