Keep track of closing socket, in WebSocket, so we don't write once the socket is closed.

sdk/lib/io/http_impl.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;
 
 class _HttpIncoming
     extends Stream<List<int>> implements StreamSink<List<int>> {
   final int _transferLength;
   final Completer _dataCompleter = new Completer();
@@ skipping 1485 matching lines @@
     return _socket.addStream(stream);
   }
 
   void addString(String string, [Encoding encoding = Encoding.UTF_8]) {
     return _socket.addString(string, encoding);
   }
 
   void destroy() => _socket.destroy();
   void add(List<int> data) => _socket.add(data);
   Future<Socket> close() => _socket.close();
+  Future<Socket> get done => _socket.done;
 }
 
 
 class _AuthenticationScheme {
   static const UNKNOWN = const _AuthenticationScheme(-1);
   static const BASIC = const _AuthenticationScheme(0);
   static const DIGEST = const _AuthenticationScheme(1);
 
   const _AuthenticationScheme(this._scheme);
 
@@ skipping 95 matching lines @@
 
 
 class _RedirectInfo implements RedirectInfo {
   const _RedirectInfo(int this.statusCode,
                       String this.method,
                       Uri this.location);
   final int statusCode;
   final String method;
   final Uri location;
 }