Add a new GetNegotiatedProtocol method to StreamSocket and implement in all subclasses.

net/socket/tcp_client_socket_libevent.cc

Index: net/socket/tcp_client_socket_libevent.cc
diff --git a/net/socket/tcp_client_socket_libevent.cc b/net/socket/tcp_client_socket_libevent.cc
index 9b47249a355cd41710e5c16fb9a64b0953b95814..b17f52f03d10fb6bccb5faf759f1dee55c4a7f0a 100644
--- a/net/socket/tcp_client_socket_libevent.cc
+++ b/net/socket/tcp_client_socket_libevent.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -733,4 +733,8 @@ base::TimeDelta TCPClientSocketLibevent::GetConnectTimeMicros() const {
   return connect_time_micros_;
 }
 
+NextProto TCPClientSocketLibevent::GetNegotiatedProtocol() const {
+  return kProtoUnknown;
+}
+
 }  // namespace net