Fix sdk/lib/io errors found by the analyzer.

sdk/lib/io/websocket_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;
 
 const String _webSocketGUID = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
 
 class _WebSocketMessageType {
   static const int NONE = 0;
@@ skipping 880 matching lines @@
   }
 
   int get readyState => _readyState;
 
   String get extensions => null;
   String get protocol => null;
   int get closeCode => _closeCode;
   String get closeReason => _closeReason;
 
   void add(data) => _sink.add(data);
-  void addError(error) => _sink.addError(error);
+  void addError(error, [StackTrace stackTrace]) =>
+      _sink.addError(error, stackTrace);
   Future addStream(Stream stream) => _sink.addStream(stream);
   Future get done => _sink.done;
 
   Future close([int code, String reason]) {
     if (_isReservedStatusCode(code)) {
       throw new WebSocketException("Reserved status code $code");
     }
     if (_outCloseCode == null) {
       _outCloseCode = code;
       _outCloseReason = reason;
@@ skipping 16 matching lines @@
            (code < WebSocketStatus.NORMAL_CLOSURE ||
             code == WebSocketStatus.RESERVED_1004 ||
             code == WebSocketStatus.NO_STATUS_RECEIVED ||
             code == WebSocketStatus.ABNORMAL_CLOSURE ||
             (code > WebSocketStatus.INTERNAL_SERVER_ERROR &&
              code < WebSocketStatus.RESERVED_1015) ||
             (code >= WebSocketStatus.RESERVED_1015 &&
              code < 3000));
   }
 }