Add the last_sent_packet_id to the candidate pair change signal

webrtc/pc/channel.h

Index: webrtc/pc/channel.h
diff --git a/webrtc/pc/channel.h b/webrtc/pc/channel.h
index e22196cae7336433a59ddc2930168d220199c9ba..e05b6e5f3f0f80b6c58f37a9a912d633aa01853b 100644
--- a/webrtc/pc/channel.h
+++ b/webrtc/pc/channel.h
@@ -209,7 +209,8 @@ class BaseChannel
 
   void OnSelectedCandidatePairChanged(
       TransportChannel* channel,
-      CandidatePairInterface* selected_candidate_pair);
+      CandidatePairInterface* selected_candidate_pair,
+      int last_sent_packet_id);
 
   bool PacketIsRtcp(const TransportChannel* channel, const char* data,
                     size_t len);