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

net/socket/socks5_client_socket.cc

Index: net/socket/socks5_client_socket.cc
diff --git a/net/socket/socks5_client_socket.cc b/net/socket/socks5_client_socket.cc
index 2c9d62a38a5898cba73c2856027af46e897501ff..dd75a4d6402dbe7e6cda7dac0ac6e898a4a151c2 100644
--- a/net/socket/socks5_client_socket.cc
+++ b/net/socket/socks5_client_socket.cc
@@ -159,6 +159,14 @@ base::TimeDelta SOCKS5ClientSocket::GetConnectTimeMicros() const {
   return base::TimeDelta::FromMicroseconds(-1);
 }
 
+NextProto SOCKS5ClientSocket::GetNegotiatedProtocol() const {
+  if (transport_.get() && transport_->socket()) {
+    return transport_->socket()->GetNegotiatedProtocol();
+  }
+  NOTREACHED();
+  return kProtoUnknown;
+}
+
 // Read is called by the transport layer above to read. This can only be done
 // if the SOCKS handshake is complete.
 int SOCKS5ClientSocket::Read(IOBuffer* buf, int buf_len,