[iOS/GN] Allow compilation with system clang.

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 110 matching lines @@
     std::unique_ptr<net::ProxyService> system_proxy_service;
     std::unique_ptr<net::HttpNetworkSession> system_http_network_session;
     std::unique_ptr<net::HttpTransactionFactory>
         system_http_transaction_factory;
     std::unique_ptr<net::URLRequestJobFactory> system_url_request_job_factory;
     std::unique_ptr<net::URLRequestContext> system_request_context;
     SystemRequestContextLeakChecker system_request_context_leak_checker;
     std::unique_ptr<net::CookieStore> system_cookie_store;
     std::unique_ptr<net::HttpUserAgentSettings> http_user_agent_settings;
     std::unique_ptr<net::NetworkQualityEstimator> network_quality_estimator;
+    std::unique_ptr<net::CTPolicyEnforcer> ct_policy_enforcer;
   };
 
   // |net_log| must either outlive the IOSChromeIOThread or be NULL.
   IOSChromeIOThread(PrefService* local_state, net_log::ChromeNetLog* net_log);
 
   ~IOSChromeIOThread() override;
 
   // Can only be called on the IO thread.
   Globals* globals();
 
@@ skipping 87 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_