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

net/http/http_network_session.cc

 // Copyright (c) 2012 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/http/http_network_session.h"
 
 #include <utility>
 
 #include "base/atomic_sequence_num.h"
 #include "base/compiler_specific.h"
@@ skipping 113 matching lines @@
       quic_idle_connection_timeout_seconds(kIdleConnectionTimeoutSeconds),
       quic_packet_reader_yield_after_duration_milliseconds(
           kQuicYieldAfterDurationMilliseconds),
       quic_disable_preconnect_if_0rtt(false),
       quic_migrate_sessions_on_network_change(false),
       quic_migrate_sessions_early(false),
       quic_allow_server_migration(false),
       quic_disable_bidirectional_streams(false),
       quic_force_hol_blocking(false),
       quic_race_cert_verification(false),
+      quic_do_not_fragment(false),
       proxy_delegate(NULL),
       enable_token_binding(false) {
   quic_supported_versions.push_back(QUIC_VERSION_35);
 }
 
 HttpNetworkSession::Params::Params(const Params& other) = default;
 
 HttpNetworkSession::Params::~Params() {}
 
 // TODO(mbelshe): Move the socket factories into HttpStreamFactory.
@@ skipping 42 matching lines @@
           params.quic_max_server_configs_stored_in_properties,
           params.quic_close_sessions_on_ip_change,
           params.disable_quic_on_timeout_with_open_streams,
           params.quic_idle_connection_timeout_seconds,
           params.quic_packet_reader_yield_after_duration_milliseconds,
           params.quic_migrate_sessions_on_network_change,
           params.quic_migrate_sessions_early,
           params.quic_allow_server_migration,
           params.quic_force_hol_blocking,
           params.quic_race_cert_verification,
+          params.quic_do_not_fragment,
           params.quic_connection_options,
           params.enable_token_binding),
       spdy_session_pool_(params.host_resolver,
                          params.ssl_config_service,
                          params.http_server_properties,
                          params.transport_security_state,
                          params.enable_spdy_ping_based_connection_checking,
                          params.spdy_session_max_recv_window_size,
                          params.spdy_stream_max_recv_window_size,
                          params.time_func,
@@ skipping 209 matching lines @@
     case base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE:
       break;
     case base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE:
     case base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL:
       CloseIdleConnections();
       break;
   }
 }
 
 }  // namespace net