Fix a browser crash on opening 'chrome://voicesearch' in guest mode.

chrome/browser/search/hotword_service_factory.h

 // Copyright 2013 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_SEARCH_HOTWORD_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_SEARCH_HOTWORD_SERVICE_FACTORY_H_
 
 #include "base/memory/singleton.h"
 #include "chrome/browser/media/media_capture_devices_dispatcher.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
@@ skipping 40 matching lines @@
   friend struct DefaultSingletonTraits<HotwordServiceFactory>;
 
   HotwordServiceFactory();
   virtual ~HotwordServiceFactory();
 
   // Overrides from BrowserContextKeyedServiceFactory:
   virtual void RegisterProfilePrefs(
       user_prefs::PrefRegistrySyncable* registry) OVERRIDE;
   virtual KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const OVERRIDE;
+  virtual content::BrowserContext* GetBrowserContextToUse(
+      content::BrowserContext* context) const OVERRIDE;
 
   // Must be called from the UI thread since the instance of
   // MediaCaptureDevicesDispatcher can only be accessed on the UI thread.
   void InitializeMicrophoneObserver();
 
   bool microphone_available() { return microphone_available_; }
 
   bool microphone_available_;
 
   DISALLOW_COPY_AND_ASSIGN(HotwordServiceFactory);
 };
 
 #endif  // CHROME_BROWSER_SEARCH_HOTWORD_SERVICE_FACTORY_H_