Switch the "Linux ChromiumOS Builder" to MB

scripts/slave/recipe_modules/chromium_tests/chromium_chromiumos.py

 # Copyright 2014 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.
 
 from . import steps
 
 SPEC = {
   'settings': {
     'build_gs_bucket': 'chromium-chromiumos-archive',
     # WARNING: src-side runtest.py is only tested with chromium CQ builders.
@@ skipping 52 matching lines @@
             gs_acl='public-read',
         ),
       ],
       'testing': {
         'platform': 'linux',
       },
     },
 
     'Linux ChromiumOS Builder': {
       'chromium_config': 'chromium',
-      'chromium_apply_config': ['chromeos', 'ninja_confirm_noop'],
+      'chromium_apply_config': ['chromeos', 'ninja_confirm_noop', 'mb'],
       'gclient_config': 'chromium',
       'chromium_config_kwargs': {
         'BUILD_CONFIG': 'Release',
         'TARGET_BITS': 64,
       },
       'bot_type': 'builder',
       'compile_targets': [
         'aura_builder',
       ],
       'testing': {
@@ skipping 151 matching lines @@
       'TARGET_CROS_BOARD': board,
     },
     'bot_type': 'builder',
     'compile_targets': [
       'chromiumos_preflight',
     ],
     'testing': {
       'platform': 'linux',
     },
   }