Fix potential crashes in NetworkHandler code

chrome/browser/io_thread.h

 // 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.
 
 #ifndef CHROME_BROWSER_IO_THREAD_H_
 #define CHROME_BROWSER_IO_THREAD_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 261 matching lines @@
   // Returns a getter for the URLRequestContext.  Only called on the UI thread.
   net::URLRequestContextGetter* system_url_request_context_getter();
 
   // Clears the host cache.  Intended to be used to prevent exposing recently
   // visited sites on about:net-internals/#dns and about:dns pages.  Must be
   // called on the IO thread.
   void ClearHostCache();
 
   void InitializeNetworkSessionParams(net::HttpNetworkSession::Params* params);
 
+  // Resets pref_proxy_config_tracker_. Required on Chrome OS to ensure that
+  // ProxyConfigServiceImpl is destroyed before NetworkHandler. Must only
+  // be called during shutdown.
+  void ShutdownPrefProxyConfigTracker();
+
   base::TimeTicks creation_time() const;
 
   // Returns true if QUIC should be enabled for data reduction proxy, either as
   // a result of a field trial or a command line flag.
   static bool ShouldEnableQuicForDataReductionProxy();
 
  private:
   // Map from name to value for all parameters associate with a field trial.
   typedef std::map<std::string, std::string> VariationParameters;
 
@@ skipping 278 matching lines @@
   bool is_quic_allowed_by_policy_;
 
   const base::TimeTicks creation_time_;
 
   base::WeakPtrFactory<IOThread> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(IOThread);
 };
 
 #endif  // CHROME_BROWSER_IO_THREAD_H_