Integrate registry_hash_store_contents with the rest of tracked prefs.

components/prefs/json_pref_store_unittest.cc

Index: components/prefs/json_pref_store_unittest.cc
diff --git a/components/prefs/json_pref_store_unittest.cc b/components/prefs/json_pref_store_unittest.cc
index 8dbbd0d2e11c897e191bb083437204f02d228ec8..7ea254a65d89e0c7fb6894d28c6bd78dccb74d24 100644
--- a/components/prefs/json_pref_store_unittest.cc
+++ b/components/prefs/json_pref_store_unittest.cc
@@ -76,8 +76,10 @@ class InterceptingPrefFilter : public PrefFilter {
       const PostFilterOnLoadCallback& post_filter_on_load_callback,
       std::unique_ptr<base::DictionaryValue> pref_store_contents) override;
   void FilterUpdate(const std::string& path) override {}
-  void FilterSerializeData(
-      base::DictionaryValue* pref_store_contents) override {}
+  base::Callback<void(bool)> FilterSerializeData(
+      base::DictionaryValue* pref_store_contents) override {
+    return base::Callback<void(bool)>();
+  }
 
   bool has_intercepted_prefs() const { return intercepted_prefs_ != NULL; }
 
@@ -1176,4 +1178,4 @@ TEST_F(JsonPrefStoreCallbackTest, TestPostWriteCallbackDuringProfileDeath) {
             write_callback_observer_.GetAndResetObservationState());
 }
 
-}  // namespace base
+}  // namespace base