Add the last_sent_packet_id to the candidate pair change signal

webrtc/base/networkroute.h

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_BASE_NETWORKROUTE_H_
 #define WEBRTC_BASE_NETWORKROUTE_H_
 
 // TODO(honghaiz): Make a directory that describes the interfaces and structs
 // the media code can rely on and the network code can implement, and both can
 // depend on that, but not depend on each other. Then, move this file to that
 // directory.
 namespace cricket {
 
 struct NetworkRoute {
   bool connected;
   uint16_t local_network_id;
   uint16_t remote_network_id;
+  int last_sent_packet_id;  // Last packet id sent on the PREVIOUS route.
 
   NetworkRoute()
-      : connected(false), local_network_id(0), remote_network_id(0) {}
+      : connected(false),
+        local_network_id(0),
+        remote_network_id(0),
+        last_sent_packet_id(-1) {}
 
   // The route is connected if the local and remote network ids are provided.
-  NetworkRoute(uint16_t local_net_id, uint16_t remote_net_id)
+  NetworkRoute(uint16_t local_net_id,
+               uint16_t remote_net_id,
+               int last_packet_id)
       : connected(true),
         local_network_id(local_net_id),
-        remote_network_id(remote_net_id) {}
+        remote_network_id(remote_net_id),
+        last_sent_packet_id(last_packet_id) {}
 
+  // |last_sent_packet_id| does not affect the NetworkRoute comparison.
   bool operator==(const NetworkRoute& nr) const {
     return connected == nr.connected &&
            local_network_id == nr.local_network_id &&
            remote_network_id == nr.remote_network_id;
   }
 
   bool operator!=(const NetworkRoute& nr) const { return !(*this == nr); }
 };
 }  // namespace cricket
 
 #endif  // WEBRTC_BASE_NETWORKROUTE_H_