static isNtpScheme_(scheme) {
    return scheme === 'urn:mpeg:dash:utc:http-ntp:2014' ||
        scheme === 'urn:mpeg:dash:utc:ntp:2014' ||
        scheme === 'urn:mpeg:dash:utc:sntp:2014';
  }
@param {string} scheme
@return {boolean}
@private