anchor.diff:    // What do the dart VM and dart2js timers do here?
     static const _minDuration = Duration.ZERO;
   
  -  _FakeTimer._(Duration duration, this._callback, this._isPeriodic, this._time,
  -      this._id)
  +  _FakeTimer._(Duration duration, this._callback, this._isPeriodic, this._time)
         : _duration = duration < _minDuration ? _minDuration : duration {
       _nextCall = _time.clock.now().add(_duration);
     }
   
  -  bool get isActive => _time._timers.containsKey(_id);
  +  bool get isActive => _time._timers.contains(this);
   
     cancel() => _time._cancelTimer(this);
   }
  
positive.code:       timer._nextCall = timer._nextCall.add(timer._duration);
      } else {
        timer._callback();
        _timers.remove(timer._id);
      }
    }
  
  
negative.code:     }
    }
  
    _cancelTimer(_FakeTimer timer) => _timers.remove(timer);
  
  }
  
  class _FakeTimer implements Timer {
  
    final Duration _duration;
    final Function _callback;
    final bool _isPeriodic;
  