Integrate registry_hash_store_contents with the rest of tracked prefs.

components/user_prefs/tracked/hash_store_contents.h

Index: components/user_prefs/tracked/hash_store_contents.h
diff --git a/components/user_prefs/tracked/hash_store_contents.h b/components/user_prefs/tracked/hash_store_contents.h
index b55a6ebe83807cc82da064c9236f7f153d31e2a0..6ef0724910e2a3a9b1d93c8729f239a728544319 100644
--- a/components/user_prefs/tracked/hash_store_contents.h
+++ b/components/user_prefs/tracked/hash_store_contents.h
@@ -14,6 +14,11 @@ class DictionaryValue;
 class Value;
 }  // namespace base
 
+enum class HashStoreContentsType : int32_t {
+  DICTIONARY_HASH_STORE_CONTENTS = 1,
+  REGISTRY_HASH_STORE_CONTENTS = 2
+};
+
 // Provides access to the contents of a preference hash store. The store
 // contains the following data:
 // Contents: a client-defined dictionary that should map preference names to
@@ -24,6 +29,9 @@ class HashStoreContents {
  public:
   virtual ~HashStoreContents() {}
 
+  // Returns the type of the HashStoreContents.
+  virtual HashStoreContentsType GetType() const = 0;
+
   // Discards all data related to this hash store.
   virtual void Reset() = 0;