_setSelectedStates() {
      this._keysSelected = {};

      for (let key in this._valueDict) {
        let option = this._valueDict[key];
        let optionIsSelected = $(option.el).prop('selected');
        $(option.optionEl)
          .find('input[type="checkbox"]')
          .prop('checked', optionIsSelected);
        if (optionIsSelected) {
          this._activateOption($(this.dropdownOptions), $(option.optionEl));
          this._keysSelected[key] = true;
        } else {
          $(option.optionEl).removeClass('selected');
        }
      }
    }
Set selected state of dropdown to match actual select element