Use a field trial to decide if QUIC should attempt to prevent packet fragmentation.

components/network_session_configurator/network_session_configurator.cc

 // Copyright 2016 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 "components/network_session_configurator/network_session_configurator.h"
 
 #include <map>
 
 #include "base/metrics/field_trial.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 208 matching lines @@
   return 0;
 }
 
 bool ShouldQuicRaceCertVerification(
     const VariationParameters& quic_trial_params) {
    return base::LowerCaseEqualsASCII(
       GetVariationParam(quic_trial_params, "race_cert_verification"),
       "true");
 }
 
+bool ShouldQuicDoNotFragment(
+    const VariationParameters& quic_trial_params) {
+   return base::LowerCaseEqualsASCII(
+      GetVariationParam(quic_trial_params, "do_not_fragment"),
+      "true");
+}
+
 bool ShouldQuicDisablePreConnectIfZeroRtt(
     const VariationParameters& quic_trial_params) {
   return base::LowerCaseEqualsASCII(
       GetVariationParam(quic_trial_params, "disable_preconnect_if_0rtt"),
       "true");
 }
 
 std::unordered_set<std::string> GetQuicHostWhitelist(
     const VariationParameters& quic_trial_params) {
   std::string whitelist =
@@ skipping 102 matching lines @@
           idle_connection_timeout_seconds;
     }
     int packet_reader_yield_after_duration_milliseconds =
         GetQuicPacketReaderYieldAfterDurationMilliseconds(quic_trial_params);
     if (packet_reader_yield_after_duration_milliseconds != 0) {
       params->quic_packet_reader_yield_after_duration_milliseconds =
           packet_reader_yield_after_duration_milliseconds;
     }
     params->quic_race_cert_verification =
         ShouldQuicRaceCertVerification(quic_trial_params);
+    params->quic_do_not_fragment =
+        ShouldQuicDoNotFragment(quic_trial_params);
     params->quic_disable_preconnect_if_0rtt =
         ShouldQuicDisablePreConnectIfZeroRtt(quic_trial_params);
     params->quic_host_whitelist = GetQuicHostWhitelist(quic_trial_params);
     params->quic_migrate_sessions_on_network_change =
         ShouldQuicMigrateSessionsOnNetworkChange(quic_trial_params);
     params->quic_migrate_sessions_early =
         ShouldQuicMigrateSessionsEarly(quic_trial_params);
     params->quic_allow_server_migration =
         ShouldQuicAllowServerMigration(quic_trial_params);
   }
@@ skipping 45 matching lines @@
   std::string http2_trial_group =
       base::FieldTrialList::FindFullName(kHttp2FieldTrialName);
   ConfigureHttp2Params(http2_trial_group, params);
 
   const std::string tfo_trial_group =
       base::FieldTrialList::FindFullName(kTCPFastOpenFieldTrialName);
   ConfigureTCPFastOpenParams(tfo_trial_group, params);
 }
 
 }  // namespace network_session_configurator