Address Ivan's comments.

sdk/lib/isolate/base.dart

 // Copyright (c) 2012, 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.
 
 class IsolateSpawnException implements Exception {
   const IsolateSpawnException(String this._s);
   String toString() => "IsolateSpawnException: '$_s'";
   final String _s;
 }
 
@@ skipping 127 matching lines @@
 
 // TODO(kasperl): Document this.
 abstract class SendPortSync {
 
   callSync(var message);
 
 }
 
 // The VM doesn't support accessing external globals in the same library. We
 // therefore create this wrapper class.
-// TODO(floitsch): add bug-number.
+// TODO(6997): Don't go through static class for external variables.
 abstract class _Isolate {
   external static ReceivePort get port;
   external static SendPort spawnFunction(void topLevelFunction());
   external static SendPort spawnUri(String uri);
 }