Add ComputeMac and ComputeSplitMacs methods to pref_hash_store.

components/user_prefs/tracked/pref_hash_store_impl.h

Index: components/user_prefs/tracked/pref_hash_store_impl.h
diff --git a/components/user_prefs/tracked/pref_hash_store_impl.h b/components/user_prefs/tracked/pref_hash_store_impl.h
index 4a2520f0d891f71f63a029a372706205f1bc5ab1..7ae2ae5f47776fc43f72605ee966428ac867700d 100644
--- a/components/user_prefs/tracked/pref_hash_store_impl.h
+++ b/components/user_prefs/tracked/pref_hash_store_impl.h
@@ -48,6 +48,11 @@ class PrefHashStoreImpl : public PrefHashStore {
   // PrefHashStore implementation.
   std::unique_ptr<PrefHashStoreTransaction> BeginTransaction(
       std::unique_ptr<HashStoreContents> storage) override;
+  std::string ComputeMac(const std::string& path,
+                         const base::Value* new_value) override;
+  std::unique_ptr<base::DictionaryValue> ComputeSplitMacs(
+      const std::string& path,
+      const base::DictionaryValue* split_values) override;
 
  private:
   class PrefHashStoreTransactionImpl;