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

net/socket/ssl_server_socket_nss.cc

Index: net/socket/ssl_server_socket_nss.cc
diff --git a/net/socket/ssl_server_socket_nss.cc b/net/socket/ssl_server_socket_nss.cc
index bb26b9cd9119cb45390622b7891316a27f9bfb98..9ba0aaaf8e0fba77a3e046c0065ca798c1f8f8df 100644
--- a/net/socket/ssl_server_socket_nss.cc
+++ b/net/socket/ssl_server_socket_nss.cc
@@ -245,6 +245,11 @@ base::TimeDelta SSLServerSocketNSS::GetConnectTimeMicros() const {
   return transport_socket_->GetConnectTimeMicros();
 }
 
+NextProto SSLServerSocketNSS::GetNegotiatedProtocol() const {
+  // NPN is not supported by this class.
+  return kProtoUnknown;
+}
+
 int SSLServerSocketNSS::InitializeSSLOptions() {
   // Transport connected, now hook it up to nss
   // TODO(port): specify rx and tx buffer sizes separately