Fix a bug in QuicSentPacketManager::ClearPreviousRetransmissions where

net/quic/quic_sent_packet_manager.cc

 // Copyright 2013 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/quic_sent_packet_manager.h"
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "net/quic/congestion_control/pacing_sender.h"
 #include "net/quic/quic_ack_notifier_manager.h"
@@ skipping 237 matching lines @@
 void QuicSentPacketManager::ClearPreviousRetransmissions(size_t num_to_clear) {
   UnackedPacketMap::iterator it = unacked_packets_.begin();
   while (it != unacked_packets_.end() && num_to_clear > 0) {
     QuicPacketSequenceNumber sequence_number = it->first;
     // If this is not a previous transmission then there is no point
     // in clearing out any further packets, because it will not affect
     // the high water mark.
     SequenceNumberSet* previous_transmissions =
         it->second.previous_transmissions;
     if (previous_transmissions == NULL) {
+      if (it->second.retransmittable_frames == NULL) {
+        // This is a current transmission, but a previous transmission has
+        // been acked, so it's safe to remove.
+        it = MarkPacketHandled(sequence_number, NOT_RECEIVED_BY_PEER);
+        --num_to_clear;
+        continue;
+      }
       break;
     }
     QuicPacketSequenceNumber newest_transmission =
         *previous_transmissions->rbegin();
     if (sequence_number == newest_transmission) {
       break;
     }
 
     DCHECK(it->second.retransmittable_frames == NULL);
     previous_transmissions->erase(sequence_number);
@@ skipping 697 matching lines @@
   }
   previous_transmissions->erase(sequence_number);
   if (previous_transmissions->size() == 1) {
     QuicPacketSequenceNumber current = *previous_transmissions->begin();
     unacked_packets_[current].previous_transmissions = NULL;
     delete previous_transmissions;
   }
 }
 
 }  // namespace net