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

tests/language/src/Factory3Test.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.
 // VMOptions=--enable_type_checks --enable_asserts
 
 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]) {
+  factory Link(T head, [Link<T> tail]) {
     return new LinkEntry<T>(head, tail);
   }
 }
 
 class AbstractLink<T> implements Link<T> {
   const AbstractLink();
   Link<T> prepend(T element) {
     print("$element");
     if (0 is T) {
       throw "0 is not a T";
@@ skipping 14 matching lines @@
   Link<Fisk> nodes = const EmptyLink<Fisk>();
   final int id;
   Fisk(this.id);
   toString() => id.toString();
 }
 
 main() {
   new Fisk(0).nodes.prepend(new Fisk(1)).prepend(new Fisk(2));
 }