Make asBroadcastStream take two callbacks.

sdk/lib/_internal/pub/lib/src/error_group.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library error_group;
 
 import 'dart:async';
 
 import 'utils.dart';
 
@@ skipping 207 matching lines @@
 class _ErrorGroupStream extends Stream {
   /// The parent [ErrorGroup].
   final ErrorGroup _group;
 
   /// Whether [this] has completed, either successfully or with an error.
   var _isDone = false;
 
   /// 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;
 
   /// Whether [this] has any listeners.
   bool get _hasListeners => _controller.hasListener;
 
   /// Creates a new [_ErrorGroupFuture] that's a child of [_group] and wraps
   /// [inner].
   _ErrorGroupStream(this._group, Stream inner)
-    : _controller = new StreamController(sync: true) {
-    this._stream = inner.isBroadcast
-        ? _controller.stream.asBroadcastStream()
-        : _controller.stream;
+    : _controller =
+          inner.isBroadcast ? new StreamController.broadcast(sync: true)
+                            : new StreamController(sync: true) {
     _subscription = inner.listen((v) {
       _controller.add(v);
     }, onError: (e) {
       _group._signalError(e);
     }, onDone: () {
       _isDone = true;
       _group._signalStreamComplete(this);
       _controller.close();
     });
   }
 
   StreamSubscription listen(void onData(value),
       {void onError(var error), void onDone(),
        bool cancelOnError}) {
-    return _stream.listen(onData,
+    return _controller.stream.listen(onData,
         onError: onError,
         onDone: onDone,
         cancelOnError: true);
   }
 
   /// Signal that an error from [_group] should be propagated through [this],
   /// unless it's already complete.
   void _signalError(var e) {
     if (_isDone) return;
     _subscription.cancel();
     // Call these asynchronously to work around issue 7913.
     new Future.value().then((_) {
       _controller.addError(e);
       _controller.close();
     });
   }
 }