Get rid of the ability to unregister preferences.

chrome/browser/ui/prefs/prefs_tab_helper.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_UI_PREFS_PREFS_TAB_HELPER_H_
 #define CHROME_BROWSER_UI_PREFS_PREFS_TAB_HELPER_H_
 
 #include "base/compiler_specific.h"
 #include "base/prefs/public/pref_change_registrar.h"
 #include "content/public/browser/notification_observer.h"
@@ skipping 10 matching lines @@
 }
 
 // Per-tab class to handle user preferences.
 class PrefsTabHelper : public content::NotificationObserver,
                        public content::WebContentsUserData<PrefsTabHelper> {
  public:
   virtual ~PrefsTabHelper();
 
   static void InitIncognitoUserPrefStore(OverlayUserPrefStore* pref_store);
   static void RegisterUserPrefs(PrefRegistrySyncable* registry);
-  static void MigrateUserPrefs(PrefService* prefs,
-                               PrefRegistrySyncable* registry);
+  static void MigrateUserPrefs(PrefService* prefs);
 
  protected:
   // Update the RenderView's WebPreferences. Exposed as protected for testing.
   virtual void UpdateWebPreferences();
 
  private:
   explicit PrefsTabHelper(content::WebContents* contents);
   friend class content::WebContentsUserData<PrefsTabHelper>;
 
   // content::NotificationObserver overrides:
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
   // Update the WebContents's RendererPreferences.
   void UpdateRendererPreferences();
 
   Profile* GetProfile();
   void OnWebPrefChanged(const std::string& pref_name);
 
   content::WebContents* web_contents_;
   content::NotificationRegistrar registrar_;
   PrefChangeRegistrar pref_change_registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefsTabHelper);
 };
 
 #endif  // CHROME_BROWSER_UI_PREFS_PREFS_TAB_HELPER_H_