Clean up old legacy preference migration logic.

components/user_prefs/tracked/pref_hash_store_impl.h

 // Copyright 2013 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_PREF_HASH_STORE_IMPL_H_
 #define COMPONENTS_USER_PREFS_TRACKED_PREF_HASH_STORE_IMPL_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 23 matching lines @@
   // |seed| and |device_id| and stores them in |contents|.
   //
   // The same |seed| and |device_id| must be used to load and validate
   // previously stored hashes in |contents|.
   PrefHashStoreImpl(const std::string& seed,
                     const std::string& device_id,
                     bool use_super_mac);
 
   ~PrefHashStoreImpl() override;
 
-  // Provides an external HashStoreContents implementation to be used.
-  // BeginTransaction() will ignore |storage| if this is provided.
-  void set_legacy_hash_store_contents(
-      std::unique_ptr<HashStoreContents> legacy_hash_store_contents);
-
   // Clears the contents of this PrefHashStore. |IsInitialized()| will return
   // false after this call.
   void Reset();
 
   // PrefHashStore implementation.
   std::unique_ptr<PrefHashStoreTransaction> BeginTransaction(
       std::unique_ptr<HashStoreContents> storage) override;
 
  private:
   class PrefHashStoreTransactionImpl;
 
   const PrefHashCalculator pref_hash_calculator_;
-  std::unique_ptr<HashStoreContents> legacy_hash_store_contents_;
   bool use_super_mac_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefHashStoreImpl);
 };
 
 #endif  // COMPONENTS_USER_PREFS_TRACKED_PREF_HASH_STORE_IMPL_H_