Clean up old legacy preference migration logic.

components/user_prefs/tracked/dictionary_hash_store_contents.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 COMPONENTS_USER_PREFS_TRACKED_DICTIONARY_HASH_STORE_CONTENTS_H_
 #define COMPONENTS_USER_PREFS_TRACKED_DICTIONARY_HASH_STORE_CONTENTS_H_
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "components/user_prefs/tracked/hash_store_contents.h"
@@ skipping 13 matching lines @@
 class DictionaryHashStoreContents : public HashStoreContents {
  public:
   // Constructs a DictionaryHashStoreContents that reads from and writes to
   // |storage|.
   explicit DictionaryHashStoreContents(base::DictionaryValue* storage);
 
   // Registers required preferences.
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
 
   // HashStoreContents implementation
-  std::string hash_store_id() const override;
   void Reset() override;
   bool IsInitialized() const override;
   const base::DictionaryValue* GetContents() const override;
   std::unique_ptr<MutableDictionary> GetMutableContents() override;
   std::string GetSuperMac() const override;
   void SetSuperMac(const std::string& super_mac) override;
 
  private:
   base::DictionaryValue* storage_;
 
   DISALLOW_COPY_AND_ASSIGN(DictionaryHashStoreContents);
 };
 
 #endif  // COMPONENTS_USER_PREFS_TRACKED_DICTIONARY_HASH_STORE_CONTENTS_H_