static replaceDrmInfo_(variants, keySystems) {
    const drmInfos = [];

    keySystems.forEach((uri, keySystem) => {
      drmInfos.push({
        keySystem: keySystem,
        licenseServerUri: uri,
        distinctiveIdentifierRequired: false,
        persistentStateRequired: false,
        audioRobustness: '',
        videoRobustness: '',
        serverCertificate: null,
        serverCertificateUri: '',
        initData: [],
        keyIds: new Set(),
      });
    });

    for (const variant of variants) {
      if (variant.video) {
        variant.video.drmInfos = drmInfos;
      }
      if (variant.audio) {
        variant.audio.drmInfos = drmInfos;
      }
    }
  }
Replace the drm info used in each variant in |variants| to reflect each
key service in |keySystems|.

@param {!Array<shaka.extern.Variant>} variants
@param {!Map<string, string>} keySystems
@private