Method enqueue

cache/base.js:56–58

* @param {!string} key * @param {!string} value * @param {!number=} priority * @return {!Promise}

(key, value, priority)

   * @return {!Promise}
   */
  enqueue(key, value, priority) {
    throw new Error('Enqueue is not overridden!');
  }

  /**
   * @param {!string} key