Fix potential crashes in NetworkHandler code

chrome/browser/chromeos/proxy_config_service_impl.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_CHROMEOS_PROXY_CONFIG_SERVICE_IMPL_H_
 #define CHROME_BROWSER_CHROMEOS_PROXY_CONFIG_SERVICE_IMPL_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
@@ skipping 34 matching lines @@
   explicit ProxyConfigServiceImpl(PrefService* profile_prefs,
                                   PrefService* local_state_prefs);
   ~ProxyConfigServiceImpl() override;
 
   // PrefProxyConfigTrackerImpl implementation.
   void OnProxyConfigChanged(ProxyPrefs::ConfigState config_state,
                             const net::ProxyConfig& config) override;
 
   // NetworkStateHandlerObserver implementation.
   void DefaultNetworkChanged(const NetworkState* network) override;
+  void OnShuttingDown() override;
 
  protected:
   friend class UIProxyConfigService;
 
   // Returns true if proxy is to be ignored for this network profile and
   // |onc_source|, e.g. this happens if the network is shared and
   // use-shared-proxies is turned off. |profile_prefs| may be NULL.
   static bool IgnoreProxy(const PrefService* profile_prefs,
                           const std::string network_profile_path,
                           onc::ONCSource onc_source);
@@ skipping 30 matching lines @@
   PrefService* local_state_prefs_;
 
   base::WeakPtrFactory<ProxyConfigServiceImpl> pointer_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ProxyConfigServiceImpl);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_PROXY_CONFIG_SERVICE_IMPL_H_