Use LeastUnacked to calculate the packet number length instead of GetLeastPacketAwaitedByPeer.

net/quic/core/quic_flags.cc

 // 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.
 
 #include "net/quic/core/quic_flags.h"
 
 // If true, it will return as soon as an error is detected while validating
 // CHLO.
 bool FLAGS_use_early_return_when_verifying_chlo = true;
 
@@ skipping 121 matching lines @@
 bool FLAGS_quic_sequencer_buffer_retire_block_in_time = true;
 
 // Remove obsolete code to force QUIC to go forward secure, now that the server
 // immediately goes forward secure.
 bool FLAGS_quic_remove_obsolete_forward_secure = false;
 
 // If true, close QUIC connection explicitly on write error due to packet being
 // too large.
 bool FLAGS_quic_close_connection_on_packet_too_large = true;
 
+// Use GetLeastUnacked when updating the packet number length, instead of
+// GetLeastPacketAwaitedByPeer.
+bool FLAGS_quic_least_unacked_packet_number_length = true;
+
 // If true, close the write side of a QUIC spdy stream when all queued bytes
 // have been written and a FIN has been sent.
 bool FLAGS_quic_close_stream_after_writing_queued_data = false;
 
 // If true, close connection with QUIC_TOO_MANY_FRAME_GAPS error when number of
 // gaps in QuicStreamSequenceBuffer exceeds allowed limit.
 bool FLAGS_quic_limit_frame_gaps_in_buffer = false;
 
 // If true, QuicSentPacketManager will use inline pacing functionality instead
 // of wrapping the SendAlgorithm with a PacingSender.
 bool FLAGS_quic_use_inline_pacing = false;