Keep an instance of QuicAckFrame in QuicConnection in order to reduce

net/quic/quic_received_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_received_packet_manager.h"
 
 #include <limits>
 #include <utility>
 
 #include "base/logging.h"
@@ skipping 219 matching lines @@
 
   // Ensure the delta is zero if approximate now is "in the past".
   ack_frame->delta_time_largest_observed =
       approximate_now < time_largest_observed_ ?
           QuicTime::Delta::Zero() :
           approximate_now.Subtract(time_largest_observed_);
 
   // Remove all packets that are too far from largest_observed to express.
   received_packet_times_.remove_if(isTooLarge(ack_frame_.largest_observed));
 
-  ack_frame->received_packet_times = received_packet_times_;
-  received_packet_times_.clear();
+  ack_frame->received_packet_times.clear();
+  ack_frame->received_packet_times.swap(received_packet_times_);
 }
 
 QuicPacketEntropyHash QuicReceivedPacketManager::EntropyHash(
     QuicPacketSequenceNumber sequence_number) const {
   return entropy_tracker_.EntropyHash(sequence_number);
 }
 
 bool QuicReceivedPacketManager::DontWaitForPacketsBefore(
     QuicPacketSequenceNumber least_unacked) {
   ack_frame_.revived_packets.erase(
@@ skipping 30 matching lines @@
   return !ack_frame_.missing_packets.empty() &&
       (ack_frame_.largest_observed -
        *ack_frame_.missing_packets.rbegin()) <= kMaxPacketsAfterNewMissing;
 }
 
 size_t QuicReceivedPacketManager::NumTrackedPackets() const {
   return entropy_tracker_.size();
 }
 
 }  // namespace net