Cleanup isolate library after frog removal.

lib/isolate/dart2js/messages.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.
 
 // Defines message visitors, serialization, and deserialization.
 
 /** Serialize [message] (or simulate serialization). */
 _serializeMessage(message) {
   if (_globalState.needSerialization) {
     return new _JsSerializer().traverse(message);
@@ skipping 144 matching lines @@
     return new _JsCopier().traverse(x);
   }
 
   // only visible for testing purposes
   static serialize(x) {
     _Serializer serializer = new _JsSerializer();
     _Deserializer deserializer = new _JsDeserializer();
     return deserializer.deserialize(serializer.traverse(x));
   }
 }