animate towards the new scroll position
function () {
      var scrollTop = content.scrollTop;
      var diff = (finalScrollTop - scrollTop);
      if (Math.abs(diff) > 3) {
        content.scrollTop += diff / 3;
        editor.animateCallback = callback;
        editor.animateTimeout = setTimeout(animate, 50);
      }
      else {
        // finished
        if (callback) {
          callback(true);
        }
        content.scrollTop = finalScrollTop;
        delete editor.animateTimeout;
        delete editor.animateCallback;
      }
    }