Reapply "Zone support for Futures, Timer, Streams."

tests/lib/async/run_zoned2_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:expect/expect.dart";
+import 'dart:async';
+import 'dart:isolate';
+
+main() {
+  // We keep a ReceivePort open until all tests are done. This way the VM will
+  // hang if the callbacks are not invoked and the test will time out.
+  var port = new ReceivePort();
+  // Ensure that `runZoned` is done when a synchronous call finishes.
+  runZonedExperimental(() => 499,
+                       onDone: port.close);
+}