Create a secondary file thread, FILE_USER_BLOCKING...

chrome/browser/browser_process_impl.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/browser_process_impl.h"
 
 #include <map>
 #include <set>
 #include <vector>
 
@@ skipping 397 matching lines @@
     CreateMetricsService();
   return metrics_service_.get();
 }
 
 IOThread* BrowserProcessImpl::io_thread() {
   DCHECK(CalledOnValidThread());
   DCHECK(io_thread_.get());
   return io_thread_.get();
 }
 
+base::Thread* BrowserProcessImpl::file_user_blocking_thread() {
+  DCHECK(CalledOnValidThread());
+  return BrowserThread::UnsafeGetBrowserThread(
+      BrowserThread::FILE_USER_BLOCKING);
+}
+
 base::Thread* BrowserProcessImpl::file_thread() {
   DCHECK(CalledOnValidThread());
   return BrowserThread::UnsafeGetBrowserThread(BrowserThread::FILE);
 }
 
 base::Thread* BrowserProcessImpl::db_thread() {
   DCHECK(CalledOnValidThread());
   return BrowserThread::UnsafeGetBrowserThread(BrowserThread::DB);
 }
 
@@ skipping 580 matching lines @@
 }
 
 void BrowserProcessImpl::OnAutoupdateTimer() {
   if (CanAutorestartForUpdate()) {
     DLOG(WARNING) << "Detected update.  Restarting browser.";
     RestartBackgroundInstance();
   }
 }
 
 #endif  // (defined(OS_WIN) || defined(OS_LINUX)) && !defined(OS_CHROMEOS)