Re-enable calls on |display_manager_| for Windows in DisplayManagerTestApi

ash/wm/system_modal_container_layout_manager_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/wm/system_modal_container_layout_manager.h"
 
 #include <memory>
 
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/shell_window_ids.h"
@@ skipping 752 matching lines @@
 
 }  // namespace
 
 TEST_F(SystemModalContainerLayoutManagerTest, BlockAllEvents) {
   InputTestDelegate delegate;
   delegate.RunTest(this);
 }
 
 // Make sure that events are properly blocked in multi displays environment.
 TEST_F(SystemModalContainerLayoutManagerTest, BlockEventsInMultiDisplays) {
+  if (!SupportsMultipleDisplays())
+    return;
+
   UpdateDisplay("500x500, 500x500");
   InputTestDelegate delegate;
   delegate.RunTest(this);
 }
 
 }  // namespace test
 }  // namespace ash