Add 'part of' in dart2js code.

lib/compiler/implementation/util/link_implementation.dart

Index: lib/compiler/implementation/util/link_implementation.dart
diff --git a/lib/compiler/implementation/util/link_implementation.dart b/lib/compiler/implementation/util/link_implementation.dart
index 783fee36d0bd13903de2b6fdf21cf4d0a31d1012..15da76f5920c82f072c2c2a3ab2da993689a159a 100644
--- a/lib/compiler/implementation/util/link_implementation.dart
+++ b/lib/compiler/implementation/util/link_implementation.dart
@@ -2,6 +2,8 @@
 // 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.
 
+part of util_implementation;
+
 class LinkIterator<T> implements Iterator<T> {
   Link<T> current;
   LinkIterator(Link<T> this.current);