Add runAsync interceptor.

tests/lib/async/intercept_run_async4_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';
+
+var events = [];
+
+body() {
+  events.add("body entry");
+  runAsync(() {
+    events.add("run async body");
+    runAsync(() {
+      events.add("run nested body");
+    });
+  });
+  return 499;
+}
+
+handler(fun) {
+  events.add("handler");
+  runAsync(fun);
+  events.add("handler done");
+}
+
+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();
+
+  // Test that body of a runAsync goes to the zone it came from.
+  var result = runZonedExperimental(body, onRunAsync: handler);
+  events.add("after");
+  runAsync(() {
+    runAsync(() {
+      Expect.listEquals(
+          ["body entry",
+           "handler", "handler done",
+           "after",
+           "run async body",
+           "handler", "handler done",
+           "run nested body"],
+          events);
+      port.close();
+    });
+  });
+}