Don't copy the QuicAckFrame into the QuicPacketGenerator. Protected by quic_dont_copy_acks.

net/quic/quic_connection.h

 // Copyright (c) 2012 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.
 //
 // The entity that handles framing writes for a Quic client or server.
 // Each QuicSession will have a connection associated with it.
 //
 // On the server side, the Dispatcher handles the raw reads, and hands off
 // packets via ProcessUdpPacket for framing and processing.
 //
@@ skipping 441 matching lines @@
   bool OnGoAwayFrame(const QuicGoAwayFrame& frame) override;
   bool OnWindowUpdateFrame(const QuicWindowUpdateFrame& frame) override;
   bool OnBlockedFrame(const QuicBlockedFrame& frame) override;
   bool OnPathCloseFrame(const QuicPathCloseFrame& frame) override;
   void OnPacketComplete() override;
 
   // QuicPacketGenerator::DelegateInterface
   bool ShouldGeneratePacket(HasRetransmittableData retransmittable,
                             IsHandshake handshake) override;
   void PopulateAckFrame(QuicAckFrame* ack) override;
+  const QuicFrame GetUpdatedAckFrame() override;
   void PopulateStopWaitingFrame(QuicStopWaitingFrame* stop_waiting) override;
 
   // QuicPacketCreator::DelegateInterface
   void OnSerializedPacket(SerializedPacket* packet) override;
   void OnUnrecoverableError(QuicErrorCode error,
                             ConnectionCloseSource source) override;
 
   // QuicSentPacketManager::NetworkChangeVisitor
   void OnCongestionWindowChange() override;
   void OnRttChange() override;
@@ skipping 577 matching lines @@
 
   // If true, multipath is enabled for this connection.
   bool multipath_enabled_;
 
   DISALLOW_COPY_AND_ASSIGN(QuicConnection);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_CONNECTION_H_