Make default argument to Iterable.join be "".

runtime/lib/typeddata.dart

 // Copyright (c) 2013, 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.
 
 // patch classes for Int8List ..... Float64List and ByteData implementations.
 
 patch class Int8List {
   /* patch */ factory Int8List(int length) {
     return new _Int8Array(length);
   }
@@ skipping 285 matching lines @@
     var len = this.length;
     for (var i = 0; i < len; i++) {
       f(this[i]);
     }
   }
 
   Iterable map(f(int element)) {
     return IterableMixinWorkaround.mapList(this, f);
   }
 
-  String join([String separator]) {
+  String join([String separator = ""]) {
     return IterableMixinWorkaround.join(this, separator);
   }
 
   dynamic reduce(dynamic initialValue,
                  dynamic combine(dynamic initialValue, element)) {
     return IterableMixinWorkaround.reduce(this, initialValue, combine);
   }
 
   dynamic fold(dynamic initialValue,
                  dynamic combine(dynamic initialValue, element)) {
@@ skipping 2769 matching lines @@
     return value;
   }
   return object;
 }
 
 
 void _throwRangeError(int index, int length) {
   String message = "$index must be in the range [0..$length)";
   throw new RangeError(message);
 }