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

net/quic/quic_received_packet_manager.h

Index: net/quic/quic_received_packet_manager.h
diff --git a/net/quic/quic_received_packet_manager.h b/net/quic/quic_received_packet_manager.h
index 173e47f0d5e28a20b2c5d164521300c13a9e549d..7985e1089b0d19550d50fd092ab9a4462b9a9b7c 100644
--- a/net/quic/quic_received_packet_manager.h
+++ b/net/quic/quic_received_packet_manager.h
@@ -116,9 +116,16 @@ class NET_EXPORT_PRIVATE QuicReceivedPacketManager
   virtual bool IsAwaitingPacket(QuicPacketNumber packet_number);
 
   // Update the |ack_frame| for an outgoing ack.
+  // TODO(ianswett): Deprecate with
+  // gfe2_reloadable_flag_quic_dont_copy_ack_frames.
   void UpdateReceivedPacketInfo(QuicAckFrame* ack_frame,
                                 QuicTime approximate_now);
 
+  // Retrieves a frame containing a QuicAckFrame.  The ack frame may not be
+  // changed outside QuicReceivedPacketManager and must be serialized before
+  // another packet is received, or it will change.
+  const QuicFrame GetUpdatedAckFrame(QuicTime approximate_now);
+
   // QuicReceivedEntropyHashCalculatorInterface
   // Called by QuicFramer, when the outgoing ack gets truncated, to recalculate
   // the received entropy hash for the truncated ack frame.