static generateTextKey_(t) {
    return shaka.util.PeriodCombiner.generateKey_([
      t.language,
      t.label,
      t.codecs,
      t.mimeType,
      t.bandwidth,
      t.roles,
    ]);
  }
@param {T} t
@return {string}
@template T
Accepts either a StreamDB or Stream type.
@private