Fix factories in Frog to correspond to the new syntax.

corelib/src/options.dart

 // 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.
 
 // Dart core library.
 
 /**
  * The Options object allows accessing the arguments which have been passed to
  * the current isolate.
  */
-interface Options factory RuntimeOptions {
+interface Options default RuntimeOptions {
   /**
    * A newly constructed Options object contains the arguments exactly as they
    * have been passed to the isolate.
    */
   Options();
 
   /**
    * Returns a list of arguments that have been passed to this isolate. Any
    * modifications to the list will be contained to the options object owning
    * this list.
    */
   List<String> get arguments();
 }