Improve error messaging of webRequest API in case of conflicts

chrome/chrome_tests.gypi

 # 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.
 {
   'variables' : {
     'pyautolib_sources': [
       'app/chrome_command_ids.h',
       'app/chrome_dll_resource.h',
       'common/automation_constants.h',
       'common/pref_names.cc',
@@ skipping 1272 matching lines @@
         'browser/extensions/extension_prefs_unittest.cc',
         'browser/extensions/extension_prefs_unittest.h',
         'browser/extensions/extension_process_manager_unittest.cc',
         'browser/extensions/extension_protocols_unittest.cc',
         'browser/extensions/extension_service_unittest.cc',
         'browser/extensions/extension_service_unittest.h',
         'browser/extensions/extension_sorting_unittest.cc',
         'browser/extensions/extension_special_storage_policy_unittest.cc',
         'browser/extensions/extension_sync_data_unittest.cc',
         'browser/extensions/extension_ui_unittest.cc',
+        'browser/extensions/extension_warning_badge_service_unittest.cc',
         'browser/extensions/extension_warning_set_unittest.cc',
         'browser/extensions/extensions_quota_service_unittest.cc',
         'browser/extensions/external_policy_loader_unittest.cc',
         'browser/extensions/menu_manager_unittest.cc',
         'browser/extensions/page_action_controller_unittest.cc',
         'browser/extensions/permissions_updater_unittest.cc',
         'browser/extensions/file_reader_unittest.cc',
         'browser/extensions/image_loading_tracker_unittest.cc',
         'browser/extensions/key_identifier_conversion_views_unittest.cc',
         'browser/extensions/management_policy_unittest.cc',
@@ skipping 3553 matching lines @@
                 '--result', '<@(_outputs)',
                 '--isolate', 'browser_tests.isolate',
               ],
             },
           ],
         },
       ],
     }],
   ],  # 'conditions'
 }