Move more from WmShell to Shell

ash/common/test/wm_shell_test_api.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_COMMON_TEST_WM_SHELL_TEST_API_H_
-#define ASH_COMMON_TEST_WM_SHELL_TEST_API_H_
-
-#include <memory>
-
-#include "base/macros.h"
-
-namespace ash {
-
-class SystemTrayDelegate;
-
-// Test API to access the internal state of the singleton WmShell.
-class WmShellTestApi {
- public:
-  WmShellTestApi();
-  ~WmShellTestApi();
-
-  void SetSystemTrayDelegate(std::unique_ptr<SystemTrayDelegate> delegate);
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(WmShellTestApi);
-};
-
-}  // namespace ash
-
-#endif  // ASH_COMMON_TEST_WM_SHELL_TEST_API_H_