  
    Polymer('paper-radio-group', {
      nextIndex: function(index) {
        var items = this.items;
        var newIndex = index;
        do {
          newIndex = (newIndex + 1) % items.length;
          if (newIndex === index) {
            break;
          }
        } while (items[newIndex].disabled);
        return newIndex;
      },
      previousIndex: function(index) {
        var items = this.items;
        var newIndex = index;
        do {
          newIndex = (newIndex || items.length) - 1;
