recognize(session, cb) {
    if (cb) {
      return this.innerRecognize(session, cb);
    }
    return new Promise((resolve, reject) => {
      this.innerRecognize(session, (err, result) => {
        if (err) {
          return reject(err);
        }
        return resolve(result);
      });
    });
  }
Given a session of a chatbot containing a message, recognize the utterance in the message.
@param {Object} session Chatbot session of the message.
@param {Function} cb Callback function.