Rewrite Futures.

tests/lib/async/future_value_chain2_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.
 
 import 'package:async_helper/async_helper.dart';
 import "package:expect/expect.dart";
 import 'dart:async';
 
+
 main() {
   asyncStart();
-  // Ensure that `runZoned`'s onError handles synchronous errors.
-  runZonedExperimental(() { throw 0; },
-                       onError: (e) {
-                         Expect.equals(0, e);
-                         asyncEnd();
-                       });
+  var errorFuture = new Future.error(499);
+  var valueChainFuture = new Future.sync(() => errorFuture);
+  // The errorFuture must not be propagated immediately as we would otherwise
+  // not have time to catch the error.
+  valueChainFuture.catchError((error) {
+    Expect.equals(499, error);
+    asyncEnd();
+  });
 }