static getInitDataFromPro_(element, systemID, keyId) {
    const Uint8ArrayUtils = shaka.util.Uint8ArrayUtils;
    const data = Uint8ArrayUtils.fromBase64(
        /** @type {string} */ (shaka.util.TXml.getTextContents(element)));
    const systemId = Uint8ArrayUtils.fromHex(systemID.replace(/-/g, ''));
    const keyIds = new Set();
    const psshVersion = 0;
    const pssh =
        shaka.util.Pssh.createPssh(data, systemId, keyIds, psshVersion);
    return [
      {
        initData: pssh,
        initDataType: 'cenc',
        keyId: keyId,
      },
    ];
  }
Gets a initData from a protection element.

@param {!shaka.extern.xml.Node} element
@param {string} systemID
@param {?string} keyId
@return {?Array<shaka.extern.InitDataOverride>}
@private