Make StreamSubscription be the active part of a stream.

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 111 matching lines @@
       future._signalError(error);
     }
 
     for (var stream in _streams) {
       if (stream._isDone || stream._hasListeners) caught = true;
       stream._signalError(error);
     }
 
     _isDone = true;
     _done._signalError(error);
-    if (!caught && !_done._hasListeners) error.throwDelayed();
+    if (!caught && !_done._hasListeners) runAsync((){ throw error; });
   }
 
   /// Notifies [this] that one of its member [Future]s is complete.
   void _signalFutureComplete(_ErrorGroupFuture future) {
     if (_isDone) return;
 
     _isDone = _futures.every((future) => future._isDone) &&
         _streams.every((stream) => stream._isDone);
     if (_isDone) _doneCompleter.complete();
   }
@@ skipping 125 matching lines @@
   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();
     });
   }
 }