static toStandardBase64(data) {
    const bytes = shaka.util.StringUtils.fromCharCode(
        shaka.util.BufferUtils.toUint8(data));
    return btoa(bytes);
  }
Convert a buffer to a base64 string. The output will be standard
alphabet as opposed to base64url safe alphabet.
@param {BufferSource} data
@return {string}
@export