Fix return type for JoinMulticast.

runtime/bin/socket_patch.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.
 
 patch class RawServerSocket {
   /* patch */ static Future<RawServerSocket> bind(address,
                                                   int port,
                                                   {int backlog: 0,
                                                    bool v6Only: false,
                                                    bool shared: false}) {
@@ skipping 1077 matching lines @@
   nativeCreateBindDatagram(List<int> addr, int port, bool reuseAddress)
       native "Socket_CreateBindDatagram";
   nativeAccept(_NativeSocket socket) native "ServerSocket_Accept";
   int nativeGetPort() native "Socket_GetPort";
   List nativeGetRemotePeer() native "Socket_GetRemotePeer";
   int nativeGetSocketId() native "Socket_GetSocketId";
   OSError nativeGetError() native "Socket_GetError";
   nativeGetOption(int option, int protocol) native "Socket_GetOption";
   bool nativeSetOption(int option, int protocol, value)
       native "Socket_SetOption";
-  bool nativeJoinMulticast(
+  OSError nativeJoinMulticast(
       List<int> addr, List<int> interfaceAddr, int interfaceIndex)
           native "Socket_JoinMulticast";
   bool nativeLeaveMulticast(
       List<int> addr, List<int> interfaceAddr, int interfaceIndex)
       native "Socket_LeaveMulticast";
 }
 
 
 class _RawServerSocket extends Stream<RawSocket>
                        implements RawServerSocket {
@@ skipping 755 matching lines @@
 Datagram _makeDatagram(List<int> data,
                        String address,
                        List<int> in_addr,
                        int port) {
   return new Datagram(
       data,
       new _InternetAddress(address, null, in_addr),
       port);
 }