Bugfix in dart:io's WebSocketTransformer implementation, correctly test async behaviour of websocke…

dart/sdk/lib/io/websocket_impl.dart

Index: dart/sdk/lib/io/websocket_impl.dart
diff --git a/dart/sdk/lib/io/websocket_impl.dart b/dart/sdk/lib/io/websocket_impl.dart
index 708af8aeeb8e1032f01b43394312827b2ee32a2c..872cd321ad7b223deadefd840311925fe9f123b8 100644
--- a/dart/sdk/lib/io/websocket_impl.dart
+++ b/dart/sdk/lib/io/websocket_impl.dart
@@ -372,6 +372,8 @@ class _WebSocketTransformerImpl implements WebSocketTransformer {
         _upgrade(request, _protocolSelector)
             .then((WebSocket webSocket) => _controller.add(webSocket))
             .catchError(_controller.addError);
+    }, onDone: () {
+      _controller.close();
     });
 
     return _controller.stream;