Wire up packet_id / send time callbacks to webrtc via libjingle.

BUG=webrtc:4173

Review URL: https://codereview.webrtc.org/1363573002

Cr-Commit-Position: refs/heads/master@{#10289}
diff --git a/webrtc/p2p/base/port.h b/webrtc/p2p/base/port.h
index dc54876..01c45f2 100644
--- a/webrtc/p2p/base/port.h
+++ b/webrtc/p2p/base/port.h
@@ -275,6 +275,9 @@
                             IceMessage* stun_msg,
                             const std::string& remote_ufrag);
 
+  // Called when a packet has been sent to the socket.
+  void OnSentPacket(const rtc::SentPacket& sent_packet);
+
   // Called when the socket is currently able to send.
   void OnReadyToSend();