Introduce PrefRegistrySyncable, simplifying PrefServiceSyncable.

chrome/browser/prefs/pref_registry.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_PREFS_PREF_REGISTRY_H_
 #define CHROME_BROWSER_PREFS_PREF_REGISTRY_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/prefs/pref_value_map.h"
@@ skipping 34 matching lines @@
   // will be invoked each time registration and/or unregistration has
   // been performed on this object.
   //
   // Calling either of these methods after a callback has already been
   // set will make the object forget the previous callback and use the
   // new one instead.
   void SetRegistrationCallback(const RegistrationCallback& callback);
   void SetUnregistrationCallback(const UnregistrationCallback& callback);
 
   // Unregisters a preference. This is going away soon.
-  virtual void DeprecatedUnregisterPreference(const char* path);
+  void DeprecatedUnregisterPreference(const char* path);
 
  protected:
   friend class base::RefCounted<PrefRegistry>;
   virtual ~PrefRegistry();
 
   // TODO(joi): Temporary until we have PrefRegistrySyncable.
   friend class PrefServiceSyncable;
 
   // Used by subclasses to register a default value for a preference.
   void RegisterPreference(const char* path, base::Value* default_value);
 
  private:
   RegistrationCallback registration_callback_;
   UnregistrationCallback unregistration_callback_;
   scoped_refptr<DefaultPrefStore> defaults_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefRegistry);
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_REGISTRY_H_