Reset the BWE when the network changes

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 759fd461db20f4fd67f52a7575ed359a4dec2b18..f50bd9b8af65162dc430fd31d54a7e23c8494489 100644
--- a/webrtc/p2p/base/p2ptransportchannel.cc
+++ b/webrtc/p2p/base/p2ptransportchannel.cc
@@ -1157,11 +1157,28 @@ void P2PTransportChannel::SwitchBestConnectionTo(Connection* conn) {
     LOG_J(LS_INFO, this) << "New best connection: "
                          << best_connection_->ToString();
     SignalRouteChange(this, best_connection_->remote_candidate());
+    if (NetworkChanged(old_best_connection, best_connection_)) {
+      SignalNetworkChanged(this, best_connection_->port()->Network()->id(), 0);
+    }

[pthatcher1, 2016/03/16 21:22:03]

I think we could use a helper method called GetNetworkRoute(const Connection*
conn) like this:

NetworkRoute route;
if (!conn) {
  route.connected = false;
} else {
  route.local_network_id = new Optional<int>(conn->port()->Network()->id());
  // TODO: Signal remote network ID.
  // route.remote_net_id = conn->remote_candidate->network_id();
}
return route;


And then we can have the code here be:

NetworkRoute old_route = GetNetworkRoute(old_conn);
NetworkRoute new_route = GetNetworkRoute(new_conn);
if (old_route != new_route) {
  SignalNetworkRouteChanged(this, old_route, new_route);
}

Of course, we need to make sure to implement operator== and operator!=

[honghaiz3, 2016/03/17 03:38:27]

Instead of Optional and CandidatePair, I just pass the pointer of
best_connection_, 
It can check if the best_connection is null and it should include every possible
information we will need, and it is sort of equivalent to SelectedCandidatePair
but without the new struct. 

+
   } else {
     LOG_J(LS_INFO, this) << "No best connection";
   }
 }
 
+bool P2PTransportChannel::NetworkChanged(const Connection* old_conn,
+                                         const Connection* new_conn) const {
+  ASSERT(new_conn != nullptr);
+  // Occasionally the best connection may be removed and a new connection is
+  // chosen afterwards, so |old_conn| may be nullptr.
+  if (old_conn == nullptr) {
+    return true;
+  }
+  // A unique network should have been created for each network key, which is
+  // generated from the network interface name, ip prefix, and ip prefix length.
+  return old_conn->port()->Network() != new_conn->port()->Network();
+}
+
 // Warning: UpdateState should eventually be called whenever a connection
 // is added, deleted, or the write state of any connection changes so that the
 // transport controller will get the up-to-date channel state. However it