Clean up old legacy preference migration logic.

components/user_prefs/tracked/dictionary_hash_store_contents.cc

 // Copyright (c) 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.
 
 #include "components/user_prefs/tracked/dictionary_hash_store_contents.h"
 
 #include "base/callback.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/values.h"
@@ skipping 42 matching lines @@
     : storage_(storage) {
 }
 
 // static
 void DictionaryHashStoreContents::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
   registry->RegisterDictionaryPref(kPreferenceMACs);
   registry->RegisterStringPref(kSuperMACPref, std::string());
 }
 
-std::string DictionaryHashStoreContents::hash_store_id() const {
-  return "";
-}
-
 void DictionaryHashStoreContents::Reset() {
   storage_->Remove(kPreferenceMACs, NULL);
 }
 
 bool DictionaryHashStoreContents::IsInitialized() const {
   return storage_->GetDictionary(kPreferenceMACs, NULL);
 }
 
 const base::DictionaryValue* DictionaryHashStoreContents::GetContents() const {
   const base::DictionaryValue* mac_dictionary = NULL;
   storage_->GetDictionary(kPreferenceMACs, &mac_dictionary);
   return mac_dictionary;
 }
 
 std::unique_ptr<HashStoreContents::MutableDictionary>
 DictionaryHashStoreContents::GetMutableContents() {
   return std::unique_ptr<MutableDictionary>(
       new MutablePreferenceMacDictionary(storage_));
 }
 
 std::string DictionaryHashStoreContents::GetSuperMac() const {
   std::string super_mac_string;
   storage_->GetString(kSuperMACPref, &super_mac_string);
   return super_mac_string;
 }
 
 void DictionaryHashStoreContents::SetSuperMac(const std::string& super_mac) {
   storage_->SetString(kSuperMACPref, super_mac);
 }