anchor.diff:      assert(_animationId != null);
       _animationId = null;
   
  -    _onTick(timeStamp);
  +    if (_startTime == null)
  +      _startTime = timeStamp;
  +
  +    _onTick(timeStamp - _startTime);
   
       // The onTick callback may have scheduled another tick already.
       if (isTicking && _animationId == null)
  
positive.code:     assert(simulation != null);
      assert(!_ticker.isTicking);
      _simulation = simulation;
      _startTime = null;
      _value = simulation.x(0.0);
      return _ticker.start();
    }
  
negative.code: import 'package:newton/newton.dart';
  import 'package:sky/src/animation/scheduler.dart';
  
  typedef _TickerCallback(Duration elapsed);
  
  /// Calls its callback once per animation frame
  class Ticker {
  