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

ash/test/ash_md_test_base.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_TEST_ASH_MD_TEST_BASE_H_
-#define ASH_TEST_ASH_MD_TEST_BASE_H_
-
-#include "ash/common/material_design/material_design_controller.h"
-#include "ash/common/test/material_design_controller_test_api.h"
-#include "ash/test/ash_test_base.h"
-
-namespace ash {
-namespace test {
-
-class AshMDTestBase
-    : public AshTestBase,
-      public testing::WithParamInterface<ash::MaterialDesignController::Mode> {
- public:
-  AshMDTestBase();
-  ~AshMDTestBase() override;
-
-  // AshTestBase:
-  void SetUp() override;
-
-  int GetMdMaximizedWindowHeightOffset();
-  int GetMdAutoHiddenShelfHeightOffset();
-
- private:
-  // The material design shelf is taller (by 1px) so use this offset to
-  // adjust the expected height of a maximized window.
-  int md_maximized_window_height_offset_ = 0;
-
-  // The material design auto hidden shelf is shorter (by 3) so use this offset
-  // to adjust the display/root window size.
-  int md_auto_hidden_shelf_height_offset_ = 0;
-
-  DISALLOW_COPY_AND_ASSIGN(AshMDTestBase);
-};
-
-}  // namespace test
-}  // namespace ash
-
-#endif  // ASH_TEST_ASH_MD_TEST_BASE_H_