Gut ash::MaterialDesignController, and remove the about:flags entry.

ash/common/test/material_design_controller_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_MATERIAL_DESIGN_CONTROLLER_TEST_API_H_
-#define ASH_COMMON_TEST_MATERIAL_DESIGN_CONTROLLER_TEST_API_H_
-
-#include "ash/common/material_design/material_design_controller.h"
-#include "base/macros.h"
-
-namespace ash {
-namespace test {
-
-// Test API to access the internal state of the MaterialDesignController class.
-// Creating an instance of this class and then destroying it preserves global
-// state in MaterialDesignController class.
-class MaterialDesignControllerTestAPI {
- public:
-  explicit MaterialDesignControllerTestAPI(MaterialDesignController::Mode mode);
-  ~MaterialDesignControllerTestAPI();
-
-  // Wrapper functions for MaterialDesignController internal functions.
-  static bool IsMaterial();
-  static bool IsMaterialNormal();
-  static bool IsMaterialExperimental();
-  static MaterialDesignController::Mode DefaultMode();
-  static void Uninitialize();
-
- private:
-  const MaterialDesignController::Mode previous_mode_;
-
-  DISALLOW_COPY_AND_ASSIGN(MaterialDesignControllerTestAPI);
-};
-
-}  // namespace test
-}  // namespace ash
-
-#endif  // ASH_COMMON_TEST_MATERIAL_DESIGN_CONTROLLER_TEST_API_H_