Rewrite Futures.

tests/lib/async/future_value_chain_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';
-import 'catch_errors.dart';
+
 
 main() {
   asyncStart();
-  // Make sure `catchErrors` shuts down the error stream when the synchronous
-  // operation is done and there isn't any asynchronous pending callback.
-  catchErrors(() {
-    return 'allDone';
-  }).listen((x) {
-      Expect.fail("Unexpected callback");
-    },
-    onDone: () {
+  var errorFuture = new Future.error(499);
+  errorFuture.catchError((x) {
+    Expect.equals(499, x);
+    var valueChainFuture = new Future.value(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();
     });
+  });
 }