Set incoming_only flag on the host side when NAT traversal is disabled.

remoting/protocol/transport_config.h

 // 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.
 
 #ifndef REMOTING_PROTOCOL_TRANSPORT_CONFIG_H_
 #define REMOTING_PROTOCOL_TRANSPORT_CONFIG_H_
 
 #include <string>
 
 namespace remoting {
 namespace protocol {
 
 struct TransportConfig {
   TransportConfig();
   ~TransportConfig();
 
-  bool nat_traversal;
+  enum NatTraversalMode {
+    // Don't use STUN or relay servers. Accept incoming P2P connection
+    // attempts, but don't initiate any. This ensures that the peer is
+    // on the same network. Note that connection will always fail if
+    // both ends use this mode.
+    NAT_TRAVERSAL_DISABLED,
+
+    // Don't use STUN or relay servers but make outgoing connections.
+    NAT_TRAVERSAL_OUTGOING,
+
+    // Active NAT traversal using STUN and relay servers.
+    NAT_TRAVERSAL_ENABLED,
+  };
+
+  NatTraversalMode nat_traversal_mode;
   std::string stun_server;
   std::string relay_server;
   std::string relay_token;
 
   // |min_port| and |max_port| specify range (inclusive) of ports used by
   // P2P sessions. Any port can be used when both values are set to 0.
   int min_port;
   int max_port;
 };
 
 }  // namespace protocol
 }  // namespace remoting
 
 #endif  // REMOTING_PROTOCOL_TRANSPORT_CONFIG_H_