Don't delay IOSink.close() with no subscription to the next instance.

sdk/lib/io/io_sink.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.
 
 part of dart.io;
 
 /**
  * Helper class to wrap a [StreamConsumer<List<int>>] and provide
  * utility functions for writing to the StreamConsumer directly. The
  * [IOSink] buffers the input given by all [StringSink] methods and will delay
@@ skipping 116 matching lines @@
   void addError(AsyncError error) {
     _controller.addError(error);
   }
 
   Future addStream(Stream<List<int>> stream) {
     if (_isBound) {
       throw new StateError("IOSink is already bound to a stream");
     }
     _isBound = true;
     // Wait for any sync operations to complete.
-    return _closeController().then((_) {
+    Future targetAddStream() {
       return _target.addStream(stream)
           .whenComplete(() {
             _isBound = false;
           });
-    });
-  }
-
-  Future _closeController() {
-    if (_controllerInstance == null) return new Future.immediate(null);
+    }
+    if (_controllerInstance == null) return targetAddStream();
     var future = _controllerCompleter.future;
     _controllerInstance.close();
-    return future;
+    return future.then((_) => targetAddStream());
   }
 
   Future close() {
     if (_isBound) {
       throw new StateError("IOSink is bound to a stream");
     }
     if (!_isClosed) {
       _isClosed = true;
       if (_controllerInstance != null) {
         _controllerInstance.close();
@@ skipping 57 matching lines @@
                 } else {
                   // No new stream. No need to close target, as it have already
                   // failed.
                   _completeDone(error: error);
                 }
               });
     }
     return _controllerInstance;
   }
 }