Wire up transport sequence number / send time callbacks to webrtc via libjingle.

webrtc/p2p/base/p2ptransportchannel.cc

Index: webrtc/p2p/base/p2ptransportchannel.cc
diff --git a/webrtc/p2p/base/p2ptransportchannel.cc b/webrtc/p2p/base/p2ptransportchannel.cc
index 2a851f5c7259cf32c22d66b149b8e059249ed939..951292b22a8b601ab9ae60748dd2d2548afa0e44 100644
--- a/webrtc/p2p/base/p2ptransportchannel.cc
+++ b/webrtc/p2p/base/p2ptransportchannel.cc
@@ -254,6 +254,8 @@ void P2PTransportChannel::AddConnection(Connection* connection) {
   connection->set_receiving_timeout(receiving_timeout_);
   connection->SignalReadPacket.connect(
       this, &P2PTransportChannel::OnReadPacket);
+  connection->SignalSentPacket.connect(this,
+                                       &P2PTransportChannel::OnSentPacket);
   connection->SignalReadyToSend.connect(
       this, &P2PTransportChannel::OnReadyToSend);
   connection->SignalStateChange.connect(
@@ -1342,6 +1344,17 @@ void P2PTransportChannel::OnReadPacket(Connection* connection,
   }
 }
 
+void P2PTransportChannel::OnSentPacket(Connection* connection,
+                                       const rtc::SentPacket& packet_sent) {
+  ASSERT(worker_thread_ == rtc::Thread::Current());
+
+  // Do not deliver if packet doesn't belong to the correct transport channel.
+  if (!FindConnection(connection))

[pthatcher1, 2015/09/25 23:24:58]

I don't think this check is necessary.  And, do we really want to iterate
through all of the connections for every packet?

[stefan-webrtc, 2015/09/28 12:10:50]

I mostly did this to follow the convention in OnReadPacket(). Should I instead
check for connection == best_connection_ as in OnReadyToSend()? I assume there
are multiple connections for one P2PTransportChannel, but only one active?

[pthatcher1, 2015/09/28 23:58:40]

I don't really think the check in OnReadPacket is necessary either. But at least
in theory it's saying "if I remove a connection, stop receiving on it".  This
would be saying "if I remove a connection, stop telling me when things that I
asked to send are not sent", which doesn't sound as useful.

[stefan-webrtc, 2015/10/02 13:29:12]

No, that doesn't make a lot of sense. Fixing.

+    return;
+
+  SignalSentPacket(this, packet_sent);
+}
+
 void P2PTransportChannel::OnReadyToSend(Connection* connection) {
   if (connection == best_connection_ && writable()) {
     SignalReadyToSend(this);