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

net/quic/quic_packet_generator.h

Index: net/quic/quic_packet_generator.h
diff --git a/net/quic/quic_packet_generator.h b/net/quic/quic_packet_generator.h
index 881d97392ceebba4ff2b2f92697d5a8a72589b9e..dfcc8a17bb0fe6dd18dc0d6f8d666cb2c0de32f8 100644
--- a/net/quic/quic_packet_generator.h
+++ b/net/quic/quic_packet_generator.h
@@ -66,6 +66,7 @@ class NET_EXPORT_PRIVATE QuicPacketGenerator {
     virtual bool ShouldGeneratePacket(HasRetransmittableData retransmittable,
                                       IsHandshake handshake) = 0;
     virtual void PopulateAckFrame(QuicAckFrame* ack) = 0;
+    virtual const QuicFrame GetUpdatedAckFrame() = 0;
     virtual void PopulateStopWaitingFrame(
         QuicStopWaitingFrame* stop_waiting) = 0;
   };
@@ -114,6 +115,9 @@ class NET_EXPORT_PRIVATE QuicPacketGenerator {
 
   bool HasQueuedFrames() const;
 
+  // Whether the pending packet has no frames in it at the moment.
+  bool IsPendingPacketEmpty() const;
+
   // Makes the framer not serialize the protocol version in sent packets.
   void StopSendingVersion();