Only consider a multichannel closed when the underlying channel closes.

lib/src/util/multi_channel.dart

 // Copyright (c) 2015, 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 test.multi_channel;
 
 import 'dart:async';
 
 import 'stream_channel.dart';
 
@@ skipping 184 matching lines @@
         onDone: () => _closeChannel(inputId, outputId));
 
     return new VirtualChannel._(
         this, outputId, streamController.stream, sinkController.sink);
   }
 
   /// Closes the virtual channel for which incoming messages have [inputId] and
   /// outgoing messages have [outputId].
   void _closeChannel(int inputId, int outputId) {
     if (_closed) return;
-    _closed = true;
+    _closed = inputId == 0;
 
     // A message without data indicates that the virtual channel has been
     // closed.
     _streamControllers.remove(inputId).close();
     _sinkControllers.remove(inputId).close();
 
     if (_innerSink == null) return;
     _innerSink.add([outputId]);
     if (_streamControllers.isEmpty) _closeInnerChannel();
   }
@@ skipping 26 matching lines @@
   /// except that it will be JSON-serializable.
   final id;
 
   final Stream stream;
   final StreamSink sink;
 
   VirtualChannel._(this._parent, this.id, this.stream, this.sink);
 
   VirtualChannel virtualChannel([id]) => _parent.virtualChannel(id);
 }