Integrate registry_hash_store_contents with the rest of tracked prefs.

components/user_prefs/tracked/dictionary_hash_store_contents.h

Index: components/user_prefs/tracked/dictionary_hash_store_contents.h
diff --git a/components/user_prefs/tracked/dictionary_hash_store_contents.h b/components/user_prefs/tracked/dictionary_hash_store_contents.h
index b14305836aafee567ab0bc6e9c45b84cf509681f..f231c257bddb7459acf06bf4ba699475bd976591 100644
--- a/components/user_prefs/tracked/dictionary_hash_store_contents.h
+++ b/components/user_prefs/tracked/dictionary_hash_store_contents.h
@@ -31,6 +31,8 @@ class DictionaryHashStoreContents : public HashStoreContents {
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
 
   // HashStoreContents implementation
+  bool IsCopyable() const override;
+  std::unique_ptr<HashStoreContents> MakeCopy() const override;
   base::StringPiece GetUMASuffix() const override;
   void Reset() override;
   bool GetMac(const std::string& path, std::string* out_value) override;