async getKeyIdFromInitSegment_(initSegmentRef) {
    let keyId = null;
    if (this.initSegmentToKidMap_.has(initSegmentRef)) {
      keyId = this.initSegmentToKidMap_.get(initSegmentRef);
    } else {
      const initSegmentRequest = shaka.util.Networking.createSegmentRequest(
          initSegmentRef.getUris(),
          initSegmentRef.getStartByte(),
          initSegmentRef.getEndByte(),
          this.config_.retryParameters);
      const requestType = shaka.net.NetworkingEngine.RequestType.SEGMENT;
      const initType =
          shaka.net.NetworkingEngine.AdvancedRequestType.INIT_SEGMENT;
      const initResponse = await this.makeNetworkRequest_(
          initSegmentRequest, requestType, {type: initType}).promise;

      initSegmentRef.setSegmentData(initResponse.data);

      keyId = shaka.media.SegmentUtils.getDefaultKID(
          initResponse.data);
      this.initSegmentToKidMap_.set(initSegmentRef, keyId);
    }
    return keyId;
  }
@param {!shaka.media.InitSegmentReference} initSegmentRef
@return {!Promise<?string>}
@private