Integrate registry_hash_store_contents with the rest of tracked prefs.

components/user_prefs/tracked/pref_hash_store_transaction.h

Index: components/user_prefs/tracked/pref_hash_store_transaction.h
diff --git a/components/user_prefs/tracked/pref_hash_store_transaction.h b/components/user_prefs/tracked/pref_hash_store_transaction.h
index b8e2cf75e75a0621ea8993e6dd18c369d79fad6e..a656fa4a60daa53e78cb2d1a7c9946d601495840 100644
--- a/components/user_prefs/tracked/pref_hash_store_transaction.h
+++ b/components/user_prefs/tracked/pref_hash_store_transaction.h
@@ -8,6 +8,8 @@
 #include <string>
 #include <vector>
 
+enum class HashStoreContentsType : int32_t;
+
 namespace base {
 class DictionaryValue;
 class Value;
@@ -41,6 +43,9 @@ class PrefHashStoreTransaction {
   // Finalizes any remaining work after the transaction has been performed.
   virtual ~PrefHashStoreTransaction() {}
 
+  // Returns the type of the store contained in this transaction.
+  virtual HashStoreContentsType GetStoreType() const = 0;
+
   // Checks |initial_value| against the existing stored value hash.
   virtual ValueState CheckValue(const std::string& path,
                                 const base::Value* initial_value) const = 0;