Add the last_sent_packet_id to the candidate pair change signal

webrtc/base/networkroute.h

Index: webrtc/base/networkroute.h
diff --git a/webrtc/base/networkroute.h b/webrtc/base/networkroute.h
index dcf9015cf72ba9a1b0b72ae05360de7b8e9f2701..95c1c088ac1b59241d7ed96373a7012d9cd463e1 100644
--- a/webrtc/base/networkroute.h
+++ b/webrtc/base/networkroute.h
@@ -21,16 +21,24 @@ 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 &&