Remove AsyncError with Expando.

tests/standalone/io/http_server_early_server_close_test.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.
 
 import "package:expect/expect.dart";
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 class Server {
   static Future<int> start() {
     return HttpServer.bind("127.0.0.1", 0).then((server) {
       server.listen((HttpRequest request) {
             Timer.run(server.close);
           }, onError: (e) {
-            Expect.fail("No server errors expected: $e");
+            String msg = "No server errors expected: $e";
+            var trace = getAttachedStackTrace(e);
+            if (trace != null) msg += "\nStackTrace: $trace";
+            Expect.fail(msg);
           });
       return server.port;
     });
   }
 }
 
 class Client {
   Client(int port) {
     ReceivePort r = new ReceivePort();
     HttpClient client = new HttpClient();
     client.get("127.0.0.1", port, "/")
         .then((HttpClientRequest request) {
           return request.close();
         })
         .then((HttpClientResponse response) {
           Expect.fail(
               "Response should not be given, as not data was returned.");
         })
         .catchError((e) {
           r.close();
         });
   }
 }
 
 main() {
   Server.start().then((port) {
     new Client(port);
   });
 }