Update from https://crrev.com/311076

net/quic/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/quic_flags.h"
 
-// TODO(rtenneti): Remove this.
-// Do not flip this flag until the flakiness of the
-// net/tools/quic/end_to_end_test is fixed.
-// If true, then QUIC connections will track the retransmission history of a
-// packet so that an ack of a previous transmission will ack the data of all
-// other transmissions.
-bool FLAGS_track_retransmission_history = false;
-
 bool FLAGS_quic_allow_oversized_packets_for_test = false;
 
 // When true, the use time based loss detection instead of nack.
 bool FLAGS_quic_use_time_loss_detection = false;
 
 // If true, it will return as soon as an error is detected while validating
 // CHLO.
 bool FLAGS_use_early_return_when_verifying_chlo = true;
 
 // If true, QUIC crypto reject message will include the reasons for rejection.
 bool FLAGS_send_quic_crypto_reject_reason = false;
 
 // If true, QUIC connections will support FEC protection of data while sending
 // packets, to reduce latency of data delivery to the application. The client
 // must also request FEC protection for the server to use FEC.
 bool FLAGS_enable_quic_fec = false;
 
 // When true, defaults to BBR congestion control instead of Cubic.
 bool FLAGS_quic_use_bbr_congestion_control = false;
 
 // If true, QUIC BBR congestion control may be enabled via Finch and/or via QUIC
 // connection options.
 bool FLAGS_quic_allow_bbr = false;
 
 // If true, truncate QUIC connection IDs if the client requests it.
-bool FLAGS_allow_truncated_connection_ids_for_quic = false;
+bool FLAGS_allow_truncated_connection_ids_for_quic = true;
 
 // Do not flip this flag.  jokulik plans more testing and additional monitoring
 // before the flag can go the auto-flip process.
 //
 // If true, record the timestamp for the last sent new packet before the call to
 // WritePacket, rather than after in QUIC.
 bool FLAGS_quic_record_send_time_before_write = false;
 
 // If true, enables the QUIC bandwidth resumption experiment (triggered by
 // Chrome/Finch).
@@ skipping 18 matching lines @@
 // store multiple addresses.
 bool FLAGS_quic_use_multiple_address_in_source_tokens = false;
 
 // If true, an attempt to send an empty data string with no FIN will return
 // early, and not create a frame.
 bool FLAGS_quic_empty_data_no_fin_early_return = true;
 
 // If true, if min RTT and/or SRTT have not yet been set then initial RTT is
 // used to initialize them in a call to QuicConnection::GetStats.
 bool FLAGS_quic_use_initial_rtt_for_stats = true;
+
+// If true, uses the last sent packet for the RTO timer instead of the earliest.
+bool FLAGS_quic_rto_uses_last_sent = true;