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:         new FakeAsync().run((async) {
            int count = 0;
            createTimer() {
              new Future.delayed(new Duration(minutes: 30), () {
                count++;
                createTimer();
              });
            }
            createTimer();
            expect(
                () => async.flushTimers(
                    timeout: new Duration(hours: 2), flushPeriodicTimers: false),
                throwsStateError);
            expect(count, 4);
          });
  
negative.code:           final log = [];
            int count = 0;
            createTimer() {
              new Future.delayed(const Duration(minutes: 30), () {
                log.add(count);
                count++;
                if (count < 4) {
  