stopPolling(options) {
    if (!this._polling) {
      return Promise.resolve();
    }
    return this._polling.stop(options);
  }
Stops polling after the last polling request resolves.
Multiple invocations do nothing if polling is already stopped.
Returning the promise of the last polling request is **deprecated**.
@param {Object} [options] Options
@param {Boolean} [options.cancel] Cancel current request
@param {String} [options.reason] Reason for stopping polling
@return {Promise}