Migrate async tests to strong

tests/lib_strong/async/intercept_schedule_microtask3_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';
+import 'catch_errors.dart';
+
+var events = [];
+
+body() {
+  events.add("body entry");
+  scheduleMicrotask(() {
+    events.add("run async body");
+  });
+  return 499;
+}
+
+handler(fun) {
+  events.add("handler");
+  scheduleMicrotask(fun);
+  events.add("handler done");
+}
+
+main() {
+  asyncStart();
+
+  // Test that scheduleMicrotask inside the scheduleMicrotask-handler goes to
+  // the parent zone.
+  var result = runZonedScheduleMicrotask(body, onScheduleMicrotask: handler);
+  events.add("after");
+  scheduleMicrotask(() {
+    Expect.listEquals(
+        ["body entry", "handler", "handler done", "after", "run async body"],
+        events);
+    asyncEnd();
+  });
+}