anchor.diff:    final NgAnimate _animate;
     var previousSet = [];
     var currentSet = [];
  -
  -  
  -      _NgClassBase(this.element, this.scope, this.mode, this.nodeAttrs, this._parser, this._animate)
  -      {
  +  Watch _watch;
  +
  +  _NgClassBase(this.element, this.scope, this.mode, this.nodeAttrs,
  +               this._parser, this._animate)
  +  {
       var prevClass;
   
       nodeAttrs.observe('class', (String newValue) {
  
positive.code:         if (oldIndex == null || mod != oldIndex % 2) {
            if (mod == mode) {
              currentSet.forEach((css) => _animate.addClass(element, css));
              //element.classes.addAll(currentSet);
            } else {
              previousSet.forEach((css) => _animate.removeClass(element, css));
              //element.classes.removeAll(previousSet);
            }
          }
        }, readOnly: true);
  
negative.code:     if (mode == null || (index != null && index % 2 == mode)) {
        previousSet.forEach((css) {
          if (!currentSet.contains(css)) {
            _animate.removeClass(element, css);
          } else {
            element.classes.remove(css);
          }
  