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 779c2009730366aba4d8fae689d340b2fb81ad71..db8d659be08b71b6d1888ea23d9d63330a2976db 100644
--- a/components/prefs/json_pref_store.cc
+++ b/components/prefs/json_pref_store.cc
@@ -323,11 +323,18 @@ void JsonPrefStore::ReportValueChanged(const std::string& key, uint32_t flags) {
   ScheduleWrite(flags);
 }
 
-void JsonPrefStore::RegisterOnNextSuccessfulWriteCallback(
-    const base::Closure& on_next_successful_write) {
+void JsonPrefStore::RegisterOnNextSuccessfulWriteReply(
+    const base::Closure& on_next_successful_write_reply) {
   DCHECK(CalledOnValidThread());
 
-  writer_.RegisterOnNextSuccessfulWriteCallback(on_next_successful_write);
+  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() {
@@ -401,8 +408,10 @@ bool JsonPrefStore::SerializeData(std::string* output) {
 
   write_count_histogram_.RecordWriteOccured();
 
-  if (pref_filter_)
-    pref_filter_->FilterSerializeData(prefs_.get());
+  if (pref_filter_) {
+    RegisterOnNextWriteSynchronousCallback(
+        pref_filter_->FilterSerializeData(prefs_.get()));
+  }
 
   JSONStringValueSerializer serializer(output);
   // Not pretty-printing prefs shrinks pref file size by ~30%. To obtain