static getInitDataFromPro_(element) {
    const proNode = shaka.util.TXml.findChildNS(
        element.node, 'urn:microsoft:playready', 'pro');
    if (!proNode || !shaka.util.TXml.getTextContents(proNode)) {
      return null;
    }

    const Uint8ArrayUtils = shaka.util.Uint8ArrayUtils;
    const textContent =
    /** @type {string} */ (shaka.util.TXml.getTextContents(proNode));
    const data = Uint8ArrayUtils.fromBase64(textContent);
    const systemId = new Uint8Array([
      0x9a, 0x04, 0xf0, 0x79, 0x98, 0x40, 0x42, 0x86,
      0xab, 0x92, 0xe6, 0x5b, 0xe0, 0x88, 0x5f, 0x95,
    ]);
    const keyIds = new Set();
    const psshVersion = 0;
    const pssh =
        shaka.util.Pssh.createPssh(data, systemId, keyIds, psshVersion);
    return [
      {
        initData: pssh,
        initDataType: 'cenc',
        keyId: element.keyId,
      },
    ];
  }
Gets a PlayReady initData from a content protection element
containing a PlayReady Pro Object

@param {shaka.dash.ContentProtection.Element} element
@return {?Array<shaka.extern.InitDataOverride>}
@private