Expose Zones.

tests/lib/async/run_zoned3_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` is done when a synchronous call throws.
-  bool sawException = false;
-  try {
-    runZonedExperimental(() { throw 0; },
-                         onDone: () {
-                           // onDone is executed synchronously.
-                           Expect.isFalse(sawException);
-                           asyncEnd();
-                         });
-  } catch (e) {
-    sawException = true;
-  }
-  Expect.isTrue(sawException);
-}