Revert of Remove support for Alt-Svc/Alternate Protocol Probability

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 120 matching lines @@
     scoped_ptr<net::HttpUserAgentSettings> http_user_agent_settings;
     scoped_ptr<net::NetworkQualityEstimator> network_quality_estimator;
     uint16_t testing_fixed_http_port;
     uint16_t testing_fixed_https_port;
     Optional<bool> enable_tcp_fast_open_for_ssl;
 
     Optional<bool> enable_spdy31;
     Optional<bool> enable_http2;
     Optional<bool> parse_alternative_services;
     Optional<bool> enable_alternative_service_with_different_host;
+    Optional<double> alternative_service_probability_threshold;
 
     Optional<bool> enable_npn;
 
     Optional<bool> enable_quic;
     Optional<bool> enable_quic_for_proxies;
     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;
@@ skipping 191 matching lines @@
 
   // Returns the QUIC version specified by |quic_version| or
   // QUIC_VERSION_UNSUPPORTED if |quic_version| is invalid.
   static net::QuicVersion ParseQuicVersion(const std::string& quic_version);
 
   // Returns the QUIC connection options specified by any flags in
   // |quic_trial_params|.
   static net::QuicTagVector GetQuicConnectionOptions(
       const VariationParameters& quic_trial_params);
 
+  // Returns the alternative service probability threshold specified by
+  // any flags in |quic_trial_params|.
+  static double GetAlternativeProtocolProbabilityThreshold(
+      const VariationParameters& quic_trial_params);
+
   static net::URLRequestContext* ConstructSystemRequestContext(
       Globals* globals,
       net::NetLog* net_log);
 
   // The NetLog is owned by the application context, to allow logging from other
   // threads during shutdown, but is used most frequently on the IO thread.
   net_log::ChromeNetLog* net_log_;
 
   // These member variables are basically global, but their lifetimes are tied
   // to the IOSChromeIOThread.  IOSChromeIOThread owns them all, despite not
@@ skipping 23 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_