Migrate async tests to strong

tests/lib_strong/async/zone_create_periodic_timer_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 'dart:async';
+
+main() {
+  Completer done = new Completer();
+  List events = [];
+
+  Expect.identical(Zone.ROOT, Zone.current);
+  Zone forked;
+  forked = Zone.current.fork(specification: new ZoneSpecification(
+      createPeriodicTimer: (Zone self, ZoneDelegate parent, Zone origin,
+                            Duration period, f(Timer timer)) {
+        events.add("forked.createPeriodicTimer");
+        return parent.createPeriodicTimer(origin, period, (Timer timer) {
+          events.add("wrapped function ${period.inMilliseconds}");
+          f(timer);
+        });
+      }));
+
+  asyncStart();
+  int tickCount = 0;
+  forked.run(() {
+    new Timer.periodic(const Duration(milliseconds: 5),
+        (Timer timer) {
+      events.add("periodic Timer $tickCount");
+      Expect.identical(forked, Zone.current);
+      tickCount++;
+      if (tickCount == 4) {
+        timer.cancel();
+        // Allow some time in case the cancel didn't work.
+        new Timer(const Duration(milliseconds: 20), done.complete);
+      }
+    });
+  });
+
+  Expect.identical(Zone.ROOT, Zone.current);
+  events.add("after createPeriodicTimer");
+
+  done.future.whenComplete(() {
+    Expect.listEquals(
+      [ "forked.createPeriodicTimer", "after createPeriodicTimer",
+        "wrapped function 5", "periodic Timer 0",
+        "wrapped function 5", "periodic Timer 1",
+        "wrapped function 5", "periodic Timer 2",
+        "wrapped function 5", "periodic Timer 3" ],
+      events);
+    asyncEnd();
+  });
+}