Integrate registry_hash_store_contents with the rest of tracked prefs.

components/user_prefs/tracked/tracked_preferences_migration.cc

 // 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.
 
 #include "components/user_prefs/tracked/tracked_preferences_migration.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 102 matching lines @@
   } else {
     CleanupPrefStore(source_store_cleaner, keys_to_clean);
   }
 }
 
 // Removes hashes for |migrated_pref_names| from |origin_pref_store| using
 // the configuration/implementation in |origin_pref_hash_store|.
 void CleanupMigratedHashes(const std::set<std::string>& migrated_pref_names,
                            PrefHashStore* origin_pref_hash_store,
                            base::DictionaryValue* origin_pref_store) {
+  DictionaryHashStoreContents dictionary_contents(origin_pref_store);
   std::unique_ptr<PrefHashStoreTransaction> transaction(
-      origin_pref_hash_store->BeginTransaction(
-          std::unique_ptr<HashStoreContents>(
-              new DictionaryHashStoreContents(origin_pref_store))));
+      origin_pref_hash_store->BeginTransaction(&dictionary_contents));
   for (std::set<std::string>::const_iterator it = migrated_pref_names.begin();
        it != migrated_pref_names.end();
        ++it) {
     transaction->ClearHash(*it);
   }
 }
 
 // Copies the value of each pref in |pref_names| which is set in |old_store|,
 // but not in |new_store| into |new_store|. Sets |old_store_needs_cleanup| to
 // true if any old duplicates remain in |old_store| and sets |new_store_altered|
 // to true if any value was copied to |new_store|.
 void MigratePrefsFromOldToNewStore(const std::set<std::string>& pref_names,
                                    base::DictionaryValue* old_store,
                                    base::DictionaryValue* new_store,
                                    PrefHashStore* new_hash_store,
                                    bool* old_store_needs_cleanup,
                                    bool* new_store_altered) {
   const base::DictionaryValue* old_hash_store_contents =
       DictionaryHashStoreContents(old_store).GetContents();
+  DictionaryHashStoreContents dictionary_contents(new_store);
   std::unique_ptr<PrefHashStoreTransaction> new_hash_store_transaction(
-      new_hash_store->BeginTransaction(std::unique_ptr<HashStoreContents>(
-          new DictionaryHashStoreContents(new_store))));
+      new_hash_store->BeginTransaction(&dictionary_contents));
 
   for (std::set<std::string>::const_iterator it = pref_names.begin();
        it != pref_names.end();
        ++it) {
      const std::string& pref_name = *it;
      const base::Value* value_in_old_store = NULL;
 
     // If the destination does not have a hash for this pref we will
     // unconditionally attempt to move it.
     bool destination_hash_missing =
@@ skipping 175 matching lines @@
   scoped_refptr<TrackedPreferencesMigrator> prefs_migrator(
       new TrackedPreferencesMigrator(
           unprotected_pref_names, protected_pref_names,
           unprotected_store_cleaner, protected_store_cleaner,
           register_on_successful_unprotected_store_write_callback,
           register_on_successful_protected_store_write_callback,
           std::move(unprotected_pref_hash_store),
           std::move(protected_pref_hash_store), unprotected_pref_filter,
           protected_pref_filter));
 }