Revert of Integrate registry_hash_store_contents with the rest of tracked prefs.

components/user_prefs/tracked/pref_hash_store.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_PREFS_TRACKED_PREF_HASH_STORE_H_
 #define COMPONENTS_PREFS_TRACKED_PREF_HASH_STORE_H_
 
 #include <memory>
 #include <string>
 
 #include "base/values.h"
 #include "components/user_prefs/tracked/pref_hash_store_transaction.h"
 
 class HashStoreContents;
-class PrefHashStoreTransaction;
 
 // Holds the configuration and implementation used to calculate and verify
 // preference MACs.
 // TODO(gab): Rename this class as it is no longer a store.
 class PrefHashStore {
  public:
   virtual ~PrefHashStore() {}
 
   // Returns a PrefHashStoreTransaction which can be used to perform a series
   // of operations on the hash store. |storage| MAY be used as the backing store
@@ skipping 13 matching lines @@
   // Computes the MAC to be associated with |path| and |split_values| in this
   // store. PrefHashStoreTransaction typically uses this internally but it's
   // also exposed for users that want to compute MACs ahead of time for
   // asynchronous operations.
   virtual std::unique_ptr<base::DictionaryValue> ComputeSplitMacs(
       const std::string& path,
       const base::DictionaryValue* split_values) = 0;
 };
 
 #endif  // COMPONENTS_PREFS_TRACKED_PREF_HASH_STORE_H_