Measure packet loss so we can use it to select ICE candidate pairs.

webrtc/p2p/base/port.h

Index: webrtc/p2p/base/port.h
diff --git a/webrtc/p2p/base/port.h b/webrtc/p2p/base/port.h
index 4d156567766746405c54cc94d4911effbc4dd2a6..7e69994f734e4d0f87a0a4f2017ea15351157010 100644
--- a/webrtc/p2p/base/port.h
+++ b/webrtc/p2p/base/port.h
@@ -20,6 +20,7 @@
 #include "webrtc/p2p/base/candidate.h"
 #include "webrtc/p2p/base/candidatepairinterface.h"
 #include "webrtc/p2p/base/jseptransport.h"
+#include "webrtc/p2p/base/packetlossestimator.h"
 #include "webrtc/p2p/base/packetsocketfactory.h"
 #include "webrtc/p2p/base/portinterface.h"
 #include "webrtc/p2p/base/stun.h"
@@ -719,6 +720,8 @@ class Connection : public CandidatePairInterface,
   int64_t receiving_unchanged_since_ = 0;
   std::vector<SentPing> pings_since_last_response_;
 
+  PacketLossEstimator packet_loss_estimator_;
+
   bool reported_;
   IceCandidatePairState state_;
   // Time duration to switch from receiving to not receiving.