Expose Zones.

tests/lib/async/zone_root_bind_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 '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 finishes.
-  runZonedExperimental(() => 499,
-                       onDone: asyncEnd);
-}
+  Expect.identical(Zone.ROOT, Zone.current);
+  Zone forked = Zone.current.fork();
+  var f = Zone.current.bindCallback(() {
+    Expect.identical(Zone.ROOT, Zone.current);
+  }, runGuarded: false);
+  forked.run(() {
+    f();
+  });
+}