Notify SystemURLRequestContextGetter before shutdown on iOS.

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 43 matching lines @@
 class URLRequestBackoffManager;
 class URLRequestContext;
 class URLRequestContextGetter;
 class URLRequestJobFactory;
 }  // namespace net
 
 namespace net_log {
 class ChromeNetLog;
 }  // namespace net_log
 
+class SystemURLRequestContextGetter;
+
 // Contains state associated with, initialized and cleaned up on, and
 // primarily used on, the IO thread.
 //
 // If you are looking to interact with the IO thread (e.g. post tasks
 // to it or check if it is the current thread), see web::WebThread.
 class IOSChromeIOThread : public web::WebThreadDelegate {
  public:
   struct Globals {
     template <typename T>
     class Optional {
@@ skipping 144 matching lines @@
   // platform and it gets SSL preferences from local_state object.
   std::unique_ptr<ssl_config::SSLConfigServiceManager>
       ssl_config_service_manager_;
 
   // These member variables are initialized by a task posted to the IO thread,
   // which gets posted by calling certain member functions of IOSChromeIOThread.
   std::unique_ptr<net::ProxyConfigService> system_proxy_config_service_;
 
   std::unique_ptr<PrefProxyConfigTracker> pref_proxy_config_tracker_;
 
-  scoped_refptr<net::URLRequestContextGetter>
+  scoped_refptr<SystemURLRequestContextGetter>
       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_