Now mode argument is correctly marked as optional in IDL itself.

lib/dom/scripts/fremontcutbuilder.py

 #!/usr/bin/python
 # Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 import database
 import databasebuilder
 import idlparser
 import logging.config
 import os.path
@@ skipping 113 matching lines @@
         'DOMCoreException': 'DOMException',
         'DOMFormData': 'FormData',
         'DOMSelection': 'Selection',
         'DOMWindow': 'Window',
         'SharedWorkerContext': 'SharedWorkerGlobalScope',
         'WorkerContext': 'WorkerGlobalScope',
       })
 
   optional_argument_whitelist = [
       ('CSSStyleDeclaration', 'setProperty', 'priority'),
-      ('IDBDatabase', 'transaction', 'mode'),
       ]
 
   # Import WebKit IDLs.
   for file_name in idl_files:
     builder.import_idl_file(file_name, webkit_options)
 
   # Import Dart idl:
   dart_options = databasebuilder.DatabaseBuilderOptions(
     idl_syntax=idlparser.FREMONTCUT_SYNTAX,
     source='Dart',
@@ skipping 63 matching lines @@
 
   for dir_name in webkit_dirs:
     dir_path = os.path.join(webcore_dir, dir_name)
     os.path.walk(dir_path, visitor, None)
 
   database_dir = os.path.join(current_dir, '..', 'database')
   return build_database(idl_files, database_dir)
 
 if __name__ == '__main__':
   sys.exit(main())