Discard old packets from the QuicSentPacketManager which are only

net/quic/quic_unacked_packet_map.h

 // 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.
 
 #ifndef NET_QUIC_QUIC_UNACKED_PACKET_MAP_H_
 #define NET_QUIC_QUIC_UNACKED_PACKET_MAP_H_
 
 #include <deque>
 
 #include "net/quic/quic_protocol.h"
@@ skipping 121 matching lines @@
   // Remove any packets no longer needed for retransmission, congestion, or
   // RTT measurement purposes.
   void RemoveObsoletePackets();
 
  private:
   void MaybeRemoveRetransmittableFrames(TransmissionInfo* transmission_info);
 
   // Returns true if the packet no longer has a purpose in the map.
   bool IsPacketUseless(QuicPacketSequenceNumber sequence_number,
                        const TransmissionInfo& info) const;
+  // Returns true if the packet is useless or it's only purpose is RTT
+  // measurement, and it's old enough that is unlikely to ever happen.
+  bool IsPacketRemovable(QuicPacketSequenceNumber sequence_number,
+                         const TransmissionInfo& info) const;
 
   QuicPacketSequenceNumber largest_sent_packet_;
   QuicPacketSequenceNumber largest_observed_;
 
   // Newly serialized retransmittable and fec packets are added to this map,
   // which contains owning pointers to any contained frames.  If a packet is
   // retransmitted, this map will contain entries for both the old and the new
   // packet. The old packet's retransmittable frames entry will be NULL, while
   // the new packet's entry will contain the frames to retransmit.
   // If the old packet is acked before the new packet, then the old entry will
   // be removed from the map and the new entry's retransmittable frames will be
   // set to NULL.
   UnackedPacketMap unacked_packets_;
   // The packet at the 0th index of unacked_packets_.
   QuicPacketSequenceNumber least_unacked_;
 
   size_t bytes_in_flight_;
   // Number of retransmittable crypto handshake packets.
   size_t pending_crypto_packet_count_;
 
   DISALLOW_COPY_AND_ASSIGN(QuicUnackedPacketMap);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_UNACKED_PACKET_MAP_H_