code: function onAnchorUpdate(newX, newY) {
           // since the callback is called before setting the new value
           // manually update the anchor point (required for updateBoundsPos)
           this.anchorPoint.setMuted(newX, newY); // then call updateBouds
  
           this.updateBoundsPos(this.pos.x, this.pos.y);
         }
docs: called when the anchor point value is changed
  @private
  @name onAnchorUpdate
  @memberOf me.Sprite.prototype
  @function