Fix websocket_impl.dart to work with websockets created by Chrome devtools.

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";
 
 // Matches _WebSocketOpcode.
 class _WebSocketMessageType {
@@ skipping 794 matching lines @@
                   userInfo: uri.userInfo,
                   host: uri.host,
                   port: uri.port,
                   path: uri.path,
                   query: uri.query,
                   fragment: uri.fragment);
     return _httpClient.openUrl("GET", uri)
       .then((request) {
         // Setup the initial handshake.
         request.headers
-            ..add(HttpHeaders.CONNECTION, "upgrade")
+            ..add(HttpHeaders.CONNECTION, "Upgrade")
             ..set(HttpHeaders.UPGRADE, "websocket")
             ..set("Sec-WebSocket-Key", nonce)
+            ..set("Cache-Control", "no-cache")
             ..set("Sec-WebSocket-Version", "13");
         if (protocols.isNotEmpty) {
           request.headers.add("Sec-WebSocket-Protocol", protocols);
         }
         return request.close();
       })
       .then((response) {
         void error(String message) {
           // Flush data.
           response.detachSocket().then((socket) {
@@ skipping 146 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));
   }
 }