anchor.diff:    /// The underlying [StreamController] for [this].
     final StreamController _controller;
   
  +  /// The controller's [Stream]. May be different than `_controller.stream` if
  +  /// the wrapped stream is a broadcasting stream.
  +  Stream _stream;
  +
     /// The [StreamSubscription] that connects the wrapped [Stream] to
     /// [_controller].
     StreamSubscription _subscription;
  
positive.code:   /// Creates a new [_ErrorGroupFuture] that's a child of [_group] and wraps
    /// [inner].
    _ErrorGroupStream(this._group, Stream inner)
      : _controller =
            inner.isBroadcast ? new StreamController.broadcast(sync: true)
                              : new StreamController(sync: true) {
      _subscription = inner.listen((v) {
        _controller.add(v);
      }, onError: (e) {
  
negative.code:   StreamSubscription listen(void onData(value),
        {void onError(var error), void onDone(),
         bool cancelOnError}) {
      return _stream.listen(onData,
          onError: onError,
          onDone: onDone,
          cancelOnError: true);
  