getResponseDelay() {
    const key = shaka.util.CmsdManager.KEYS_.RESPONSE_DELAY;
    if (!this.config_.enabled || !this.dynamicParams_ ||
        !this.dynamicParams_.has(key)) {
      return null;
    }
    return /** @type {number} */(this.dynamicParams_.get(key));
  }
Returns the response delay in milliseconds. If there is no response delay
or it's not enabled, it returns null.

@return {?number}
@export