Remove AsyncError with Expando.

tests/standalone/io/string_transformer_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";
 import "dart:utf";
 
@@ skipping 179 matching lines @@
   var controller = new StreamController();
   var errors = 0;
   var stream = controller.stream
     .transform(new StringDecoder())
     .transform(new LineTransformer());
   stream.listen(
       (_) {},
       onDone: () {
         Expect.equals(1, errors);
       },
-      onError: (e) {
+      onError: (error) {
         errors++;
-        Expect.isTrue(e.error is TestException);
+        Expect.isTrue(error is TestException);
       });
   controller.addError(new TestException());
   controller.close();
 }
 
 testLatin1EncoderError() {
   List<int> data = [0x01,
                     0x7f,
                     0x44, 0x61, 0x72, 0x74,
                     0x80,
                     0xff,
                     0x100];
   var controller = new StreamController();
   controller.add(new String.fromCharCodes(data));
   controller.close();
   var stream = controller.stream
     .transform(new StringEncoder(Encoding.ISO_8859_1));
   stream.listen(
     (s) {
       Expect.fail("data not expected");
     },
     onError: (error) {
-      Expect.isTrue(error.error is FormatException);
+      Expect.isTrue(error is FormatException);
     });
 
 }
 
 main() {
   testUtf8();
   testLatin1();
   testAscii();
   testReadLine1();
   testReadLine2();
   testErrorHandler();
   testLatin1EncoderError();
 }