msgLit(keys, variables, options) {
      if (this.__localizeMessageSync) {
        return this._localizeManager.msg(keys, variables, options);
      }

      if (!this.localizeNamespacesLoaded) {
        return '';
      }

      return until(
        this.localizeNamespacesLoaded.then(() =>
          this._localizeManager.msg(keys, variables, options),
        ),
        nothing,
      );
    }
@param {string | string[]} keys
@param {Object.<string,?>} [variables]
@param {Object} [options]
@param {string} [options.locale]
@returns {string | DirectiveResult}