Make IOSink implement StringSink

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 641 matching lines @@
     } else if (dataLength > 125) {
       header[index++] = 126;
       lengthBytes = 2;
     }
     // Write the length in network byte order into the header.
     for (int i = 0; i < lengthBytes; i++) {
       header[index++] = dataLength >> (((lengthBytes - 1) - i) * 8) & 0xFF;
     }
     assert(index == headerSize);
     try {
-      _socket.add(header);
+      _socket.writeBytes(header);
       if (data != null) {
-        _socket.add(data);
+        _socket.writeBytes(data);
       }
     } catch (_) {
       // The socket can be closed before _socket.done have a chance
       // to complete.
       _writeClosed = true;
     }
   }
 }