use additional_expectations as a command parameter

masters/master.chromium.webkit/master_mac_webkit_pinned_cfg.py

 # Copyright (c) 2012 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.
 
 # WebKit test builders using the Skia graphics library.
 
 from master import master_config
 from master.factory import chromium_factory
 
 import config
@@ skipping 58 matching lines @@
 F('f_webkit_rel_tests', mac().ChromiumFactory(
     slave_type='Tester',
     build_url=rel_archive,
     tests=[
       'test_shell',
       'webkit',
       'webkit_lint',
       'webkit_unit',
     ],
     factory_properties={
-      'additional_expectations_files': [
+      'additional_expectations': [
         ['webkit', 'tools', 'layout_tests', 'test_expectations.txt' ],
       ],
       'archive_webkit_results': ActiveMaster.is_production_host,
       'generate_gtest_json': True,
       'layout_test_platform': 'chromium-mac',
       'test_results_server': 'test-results.appspot.com',
     }))
 
 ################################################################################
 ##
 ################################################################################
 
 def Update(_config, active_master, c):
   return helper.Update(c)