Integrate registry_hash_store_contents with the rest of tracked prefs.

components/prefs/json_pref_store.cc

Index: components/prefs/json_pref_store.cc
diff --git a/components/prefs/json_pref_store.cc b/components/prefs/json_pref_store.cc
index 9dd313438ca3a7affa50ac5ec9504b6cc621d746..970c78e6602df804b0b92850f9880e0c452d6920 100644
--- a/components/prefs/json_pref_store.cc
+++ b/components/prefs/json_pref_store.cc
@@ -330,6 +330,13 @@ void JsonPrefStore::RegisterOnNextSuccessfulWriteReply(
   writer_.RegisterOnNextSuccessfulWriteReply(on_next_successful_write_reply);
 }
 
+void JsonPrefStore::RegisterOnNextWriteSynchronousCallback(
+    const base::Callback<void(bool success)>& on_next_write_callback) {
+  DCHECK(CalledOnValidThread());
+
+  writer_.RegisterOnNextWriteSynchronousCallback(on_next_write_callback);
+}
+
 void JsonPrefStore::ClearMutableValues() {
   NOTIMPLEMENTED();
 }
@@ -401,8 +408,12 @@ bool JsonPrefStore::SerializeData(std::string* output) {
 
   write_count_histogram_.RecordWriteOccured();
 
-  if (pref_filter_)
-    pref_filter_->FilterSerializeData(prefs_.get());
+  if (pref_filter_) {
+    base::Callback<void(bool)> pref_filter_post_write_callback =
+        pref_filter_->FilterSerializeData(prefs_.get());
+    if (!pref_filter_post_write_callback.is_null())
+      RegisterOnNextWriteSynchronousCallback(pref_filter_post_write_callback);
+  }
 
   JSONStringValueSerializer serializer(output);
   // Not pretty-printing prefs shrinks pref file size by ~30%. To obtain