anchor.diff:            new Future(() {
               log.add(2);
             });
  -          new Timer.periodic(new Duration(seconds: 1), (_) {
  +          new Timer.periodic(const Duration(seconds: 1), (_) {
               log.add(2);
             });
             async.flushMicrotasks();
  
positive.code:       test('should flush periodic timers', () {
          new FakeAsync().run((async) {
            int count = 0;
            new Timer.periodic(new Duration(minutes: 30), (Timer timer) {
              if (count == 3) {
                timer.cancel();
              }
              count++;
            });
            async.flushTimers(timeout: new Duration(hours: 20));
            expect(count, 4);
          });
        });
  
negative.code:         new FakeAsync().run((async) {
            expect(async.periodicTimerCount, 0);
            Timer timer =
                new Timer.periodic(const Duration(minutes: 30), (Timer timer) {});
            expect(async.periodicTimerCount, 1);
            new Timer.periodic(const Duration(minutes: 20), (Timer timer) {});
            expect(async.periodicTimerCount, 2);
            async.elapse(const Duration(minutes: 20));
            expect(async.periodicTimerCount, 2);
            timer.cancel();
            expect(async.periodicTimerCount, 1);
  