Moved JsonPrefStore to use SequencedWorkerPool

chrome/browser/prefs/pref_service.cc

Index: chrome/browser/prefs/pref_service.cc
diff --git a/chrome/browser/prefs/pref_service.cc b/chrome/browser/prefs/pref_service.cc
index 40ae0d30b0261aae0a69afaa4011fde313392145..1eb80b4a76ce15149a345acd904b2ffaacdf951e 100644
--- a/chrome/browser/prefs/pref_service.cc
+++ b/chrome/browser/prefs/pref_service.cc
@@ -123,6 +123,7 @@ PrefServiceBase* PrefServiceBase::FromBrowserContext(BrowserContext* context) {
 // static
 PrefService* PrefService::CreatePrefService(
     const FilePath& pref_filename,
+    base::SequencedTaskRunner* pref_io_task_runner,
     policy::PolicyService* policy_service,
     PrefStore* extension_prefs,
     bool async) {
@@ -156,8 +157,7 @@ PrefService* PrefService::CreatePrefService(
   CommandLinePrefStore* command_line =
       new CommandLinePrefStore(CommandLine::ForCurrentProcess());
   JsonPrefStore* user = new JsonPrefStore(
-      pref_filename,
-      BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE));
+      pref_filename, pref_io_task_runner);
   DefaultPrefStore* default_pref_store = new DefaultPrefStore();
 
   PrefNotifierImpl* pref_notifier = new PrefNotifierImpl();