Updates dartc to recognize 'default' keyword on interface and updated factory method syntax

tests/language/src/Factory2Test.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 test program for testing factories.
 
 interface Link<T> extends Iterable<T> factory LinkFactory<T> {
   Link(T head, [Link<T> tail]);
   Link<T> prepend(T element);
 }
 
-interface EmptyLink<T> extends Link<T> factory LinkTail<T> {
+interface EmptyLink<T> extends Link<T> default LinkTail<T> {
   const EmptyLink();
 }
 
 class LinkFactory<T> {
   factory Link(head, [Link tail]) {
   }
 }
 
 class AbstractLink<T> implements Link<T> {
   const AbstractLink();
@@ skipping 13 matching lines @@
 class Fisk {
  Link<String> nodes = const EmptyLink();
 }
 
 main() {
   new Fisk();
   new EmptyLink<String>().prepend('hest');
   const EmptyLink<String>().prepend('fisk');
 }