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

ash/common/test/BUILD.gn

 # 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.
 
 static_library("test_support") {
   testonly = true
   sources = [
     "ash_test.cc",
     "ash_test.h",
     "ash_test_impl.h",
-    "material_design_controller_test_api.cc",
-    "material_design_controller_test_api.h",
     "test_palette_delegate.cc",
     "test_palette_delegate.h",
     "test_session_state_delegate.cc",
     "test_session_state_delegate.h",
     "test_shelf_delegate.cc",
     "test_shelf_delegate.h",
     "test_shelf_item_delegate.cc",
     "test_shelf_item_delegate.h",
     "test_system_tray_delegate.cc",
     "test_system_tray_delegate.h",
@@ skipping 17 matching lines @@
 
     # TODO: this is for ui/wm/public/window_types.h, which is in aura.
     # http://crbug.com/654078.
     "//ui/aura",
     "//ui/display/manager",
     "//ui/gfx/geometry",
     "//ui/views",
     "//ui/wm",
   ]
 }