chromeos: Makes AshTestBase/Helper target mash when appropriate

ash/mus/test/wm_test_helper.h

 // Copyright 2016 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.
 
 #ifndef ASH_MUS_TEST_WM_TEST_HELPER_H_
 #define ASH_MUS_TEST_WM_TEST_HELPER_H_
 
 #include <memory>
 
 #include "ash/mus/window_manager_application.h"
 #include "base/macros.h"
 #include "ui/aura/test/mus/test_window_tree_client_setup.h"
 
 namespace aura {
 class WindowTreeClientPrivate;
 }
 
 namespace base {
 class MessageLoop;
 class SequencedWorkerPoolOwner;
 }
 
-namespace ui {
-class WindowTreeClientPrivate;
-}
-
 namespace views {
 class ViewsDelegate;
 }
 
 namespace ash {
 
 class RootWindowController;
 
 namespace mus {
 
@@ skipping 46 matching lines @@
 
   std::unique_ptr<base::SequencedWorkerPoolOwner> blocking_pool_owner_;
 
   DISALLOW_COPY_AND_ASSIGN(WmTestHelper);
 };
 
 }  // namespace mus
 }  // namespace ash
 
 #endif  // ASH_MUS_TEST_WM_TEST_HELPER_H_