code: function addClass(element, className) {
      if ((' ' + element.className + ' ').indexOf(' ' + className + ' ') === -1) {
        element.className += (element.className ? ' ' : '') + className;
      }  
    }
docs: Adds class to an element
  @method addClass
  @memberOf fabric.util
  @param {HTMLElement} element Element to add class to
  @param {String} className Class to add to an element