Add more information to LOG(DFATAL) in QUIC's tcp_loss_algorithm.

net/quic/congestion_control/tcp_loss_algorithm.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/quic/congestion_control/tcp_loss_algorithm.h"
 
 #include "net/quic/congestion_control/rtt_stats.h"
 #include "net/quic/quic_protocol.h"
 
 namespace net {
@@ skipping 28 matching lines @@
       rtt_stats.SmoothedRtt().Multiply(kEarlyRetransmitLossDelayMultiplier);
   QuicPacketSequenceNumber sequence_number = unacked_packets.GetLeastUnacked();
   for (QuicUnackedPacketMap::const_iterator it = unacked_packets.begin();
        it != unacked_packets.end() && sequence_number <= largest_observed;
        ++it, ++sequence_number) {
     if (!it->in_flight) {
       continue;
     }
 
     LOG_IF(DFATAL, it->nack_count == 0)
-        << "All packets less than largest observed should have been nacked.";
+        << "All packets less than largest observed should have been nacked."
+        << "sequence_number:" << sequence_number
+        << " largest_observed:" << largest_observed;
     if (it->nack_count >= kNumberOfNacksBeforeRetransmission) {
       lost_packets.insert(sequence_number);
       continue;
     }
 
     // Only early retransmit(RFC5827) when the last packet gets acked and
     // there are retransmittable packets in flight.
     // This also implements a timer-protected variant of FACK.
     if (it->retransmittable_frames &&
         unacked_packets.largest_sent_packet() == largest_observed) {
@@ skipping 11 matching lines @@
   }
 
   return lost_packets;
 }
 
 QuicTime TCPLossAlgorithm::GetLossTimeout() const {
   return loss_detection_timeout_;
 }
 
 }  // namespace net