Add Future.timeout.

tests/lib/async/future_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.
 
 library future_test;
 
 import 'package:async_helper/async_helper.dart';
 import "package:expect/expect.dart";
 import 'dart:async';
 
@@ skipping 790 matching lines @@
 
 /// A Future that isn't recognizable as a _Future.
 class CustomFuture<T> implements Future<T> {
   Future _realFuture;
   CustomFuture(this._realFuture);
   Future then(action(result), {Function onError}) =>
       _realFuture.then(action, onError: onError);
   Future catchError(Function onError, {bool test(e)}) =>
       _realFuture.catchError(onError, test: test);
   Future whenComplete(action()) => _realFuture.whenComplete(action);
+  Future timeout(Duration timeLimit, [void onTimeout()]) =>
+      _realFuture.timeout(timeLimit, onTimeout);
   Stream asStream() => _realFuture.asStream();
   String toString() => "CustomFuture@${_realFuture.hashCode}";
   int get hashCode => _realFuture.hashCode;
 }