chrome: Cleanup class/struct forward declarations

chrome/browser/autofill/validation_rules_storage_factory.h

 // Copyright 2014 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_AUTOFILL_VALIDATION_RULES_STORAGE_FACTORY_H_
 #define CHROME_BROWSER_AUTOFILL_VALIDATION_RULES_STORAGE_FACTORY_H_
 
 #include <memory>
 
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 
 namespace i18n {
 namespace addressinput {
 class Storage;
 }
 }
 
 class JsonPrefStore;
-class PersistentPrefStore;
 
 namespace autofill {
 
 // Creates Storage objects, all of which are backed by a common pref store.
 class ValidationRulesStorageFactory {
  public:
   static std::unique_ptr<::i18n::addressinput::Storage> CreateStorage();
 
  private:
   friend struct base::DefaultLazyInstanceTraits<ValidationRulesStorageFactory>;
 
   ValidationRulesStorageFactory();
   ~ValidationRulesStorageFactory();
 
   scoped_refptr<JsonPrefStore> json_pref_store_;
 
   DISALLOW_COPY_AND_ASSIGN(ValidationRulesStorageFactory);
 };
 
 }  // namespace autofill
 
 #endif  // CHROME_BROWSER_AUTOFILL_VALIDATION_RULES_STORAGE_FACTORY_H_