anchor.diff:     */
     final core.int chunkSize;
   
  +  /**
  +   * Function for determining the [core.Duration] to wait before making the
  +   * next attempt. See [ExponentialBackoff] for an example.
  +   */
  +  final core.Function backoffFunction;
  +
     ResumableUploadOptions({this.numberOfAttempts: 3,
  -                          this.chunkSize: 1024 * 1024}) {
  +                          this.chunkSize: 1024 * 1024,
  +                          core.Function backoffFunction})
  +      : backoffFunction = backoffFunction == null ?
  +          ExponentialBackoff : backoffFunction {
       // See e.g. here:
       // https://developers.google.com/maps-engine/documentation/resumable-upload
       //
  
positive.code:           });
  
            test('stream-big-block-parts--with-server-error-recovery', () {
              var options = new ResumableUploadOptions(
                  chunkSize: 256 * 1024, numberOfAttempts: 4);
              runTest(1, 1024 * 1024,
                      [1,
                       256*1024-1,
  
negative.code:   core.String toString()
        => 'DetailedApiRequestError(status: $status, message: $message)';
  }
  """;
  
  
  