addKeyIdsData(base64) {
    if (!this.initData) {
      this.initData = [];
    }

    const buffer = shaka.util.Uint8ArrayUtils.fromBase64(base64);
    this.initData.push({initData: buffer, initDataType: 'keyids'});
  }
Adds a new 'keyids' init data to the current DRM info.

@param {string} base64