Remove AsyncError with Expando.

tests/standalone/io/secure_socket_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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 import "package:expect/expect.dart";
@@ skipping 38 matching lines @@
       socket.listen(
         (List<int> data) {
           body.addAll(data);
         },
         onDone: () {
           Expect.isTrue(body.length > 100, "$body\n${body.length}");
           Expect.equals(72, body[0]);
           Expect.equals(9, body[body.length - 1]);
           server.close();
         },
-        onError: (e) => Expect.fail("Unexpected error $e"));
+        onError: (e) {
+          String msg = "Unexpected error $e";
+          var trace = getAttachedStackTrace(e);
+          if (trace != null) msg += "\nStackTrace: $trace";
+          Expect.fail(msg);
+        });
     });
   });
 }