Add deprecated WebSocket constructor.

sdk/lib/io/websocket.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;
 
 /**
  * Web socket status codes used when closing a web socket connection.
  */
 abstract class WebSocketStatus {
@@ skipping 115 matching lines @@
 
   /**
    * Create a new web socket connection. The URL supplied in [url]
    * must use the scheme [:ws:] or [:wss:]. The [protocols] argument is
    * specifying the subprotocols the client is willing to speak.
    */
   static Future<WebSocket> connect(String url,
                                    {List<String> protocols: const []}) =>
       _WebSocketImpl.connect(url, protocols);
 
+  @Deprecated('This constructor will be removed in Dart 2.0. Use `implements`'
+      ' instead of `extends` if implementing this abstract class.')
+  WebSocket();
+
   /**
    * Creates a WebSocket from an already-upgraded socket.
    *
    * The initial WebSocket handshake must have occurred prior to this call. A
    * WebSocket client can automatically perform the handshake using
    * [WebSocket.connect], while a server can do so using
    * [WebSocketTransformer.upgrade]. To manually upgrade an [HttpRequest],
    * [HttpRequest.detachSocket] may be called.
    *
    * [protocol] should be the protocol negotiated by this handshake, if any.
@@ skipping 64 matching lines @@
    */
   Future addStream(Stream stream);
 }
 
 
 class WebSocketException implements IOException {
   final String message;
   const WebSocketException([this.message = ""]);
   String toString() => "WebSocketException: $message";
 }