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

ash/test/display_manager_test_api.cc

Index: ash/test/display_manager_test_api.cc
diff --git a/ash/test/display_manager_test_api.cc b/ash/test/display_manager_test_api.cc
index 581898462d165cc34a04f36b3cae19253e74687c..167c8fae0aea4ccc4970d865448ab2fe8345f0ae 100644
--- a/ash/test/display_manager_test_api.cc
+++ b/ash/test/display_manager_test_api.cc
@@ -109,12 +109,9 @@ void DisplayManagerTestApi::UpdateDisplay(const std::string& display_specs) {
     }
   }
 
-// TODO(msw): This seems to cause test hangs on Windows. http://crbug.com/584038
-#if !defined(OS_WIN)
   display_manager_->OnNativeDisplaysChanged(display_info_list);
   display_manager_->UpdateInternalDisplayModeListForTest();
   display_manager_->RunPendingTasksForTest();
-#endif
 }
 
 int64_t DisplayManagerTestApi::SetFirstDisplayAsInternalDisplay() {