QUIC - Add back to code to experiment with delay_tcp_race. By default,

ios/chrome/browser/ios_chrome_io_thread.h

 // Copyright 2015 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.
 
 #ifndef IOS_CHROME_BROWSER_IOS_CHROME_IO_THREAD_H_
 #define IOS_CHROME_BROWSER_IOS_CHROME_IO_THREAD_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 137 matching lines @@
     Optional<bool> quic_always_require_handshake_confirmation;
     Optional<bool> quic_disable_connection_pooling;
     Optional<float> quic_load_server_info_timeout_srtt_multiplier;
     Optional<bool> quic_enable_connection_racing;
     Optional<bool> quic_enable_non_blocking_io;
     Optional<bool> quic_disable_disk_cache;
     Optional<bool> quic_prefer_aes;
     Optional<int> quic_max_number_of_lossy_connections;
     Optional<float> quic_packet_loss_threshold;
     Optional<int> quic_socket_receive_buffer_size;
+    Optional<bool> quic_delay_tcp_race;
     Optional<size_t> quic_max_packet_length;
     net::QuicTagVector quic_connection_options;
     Optional<std::string> quic_user_agent_id;
     Optional<net::QuicVersionVector> quic_supported_versions;
     Optional<bool> quic_close_sessions_on_ip_change;
   };
 
   // |net_log| must either outlive the IOSChromeIOThread or be NULL.
   IOSChromeIOThread(PrefService* local_state, net_log::ChromeNetLog* net_log);
 
@@ skipping 143 matching lines @@
   // closed and is considered as a lossy connection. Returns 0 if the default
   // value should be used.
   static float GetQuicPacketLossThreshold(
       const VariationParameters& quic_trial_params);
 
   // Returns the size of the QUIC receive buffer to use, or 0 if
   // the default should be used.
   static int GetQuicSocketReceiveBufferSize(
       const VariationParameters& quic_trial_params);
 
+  // Returns true if QUIC should delay TCP connection when QUIC works.
+  static bool ShouldQuicDelayTcpRace(
+      const VariationParameters& quic_trial_params);
+
   // Returns true if QUIC should close sessions when any of the client's
   // IP addresses change.
   static bool ShouldQuicCloseSessionsOnIpChange(
       const VariationParameters& quic_trial_params);
 
   // Returns the maximum length for QUIC packets, based on any flags in the
   // field trial.  Returns 0 if there is an error parsing any of the options,
   // or if the default value should be used.
   static size_t GetQuicMaxPacketLength(
       const VariationParameters& quic_trial_params);
@@ skipping 48 matching lines @@
       system_url_request_context_getter_;
 
   const base::TimeTicks creation_time_;
 
   base::WeakPtrFactory<IOSChromeIOThread> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(IOSChromeIOThread);
 };
 
 #endif  // IOS_CHROME_BROWSER_IOS_CHROME_IO_THREAD_H_