Remove AsyncError with Expando.

tests/isolate/global_error_handler_stream2_test.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.
 
 library test;
 
 import 'package:expect/expect.dart';
 import 'dart:async';
 import 'dart:isolate';
 
 runTest() {
   IsolateSink mainIsolate;
   stream.listen((msg) {
     mainIsolate = msg;
     throw new RuntimeError("ignore exception");
   }, onDone: () {
     mainIsolate.add("received done");
     mainIsolate.close();
   });
 }
 
 bool globalErrorHandler(IsolateUnhandledException e) {
   var source = e.source;
-  if (source is AsyncError) {
-    source = source.error;
-  }
   return source is RuntimeError && source.message == "ignore exception";
 }
 
 main() {
   var keepRunningBox = new MessageBox();
   // Make sure this test doesn't last longer than 2 seconds.
   var timer = new Timer(const Duration(seconds: 2), () { throw "failed"; });
 
   var box = new MessageBox();
   IsolateSink otherIsolate = streamSpawnFunction(runTest, globalErrorHandler);
   otherIsolate.add(box.sink);
   // The previous event should have been handled entirely, but the current
   // implementations don't guarantee that and might mix the done event with
   // the handling of the previous event. We therefore delay the closing.
   // Note: if the done is sent too early it won't lead to failing tests, but
   // just won't make sure that the globalErrorHandler works.
   new Timer(const Duration(milliseconds: 10), otherIsolate.close);
   box.stream.single.then((msg) {
     Expect.equals("received done", msg);
     timer.cancel();
     keepRunningBox.stream.close();
   });
 }