Redirect BrowserThread::FILE at USER_VISIBLE instead of BACKGROUND priority.

content/browser/browser_main_loop.cc

Index: content/browser/browser_main_loop.cc
diff --git a/content/browser/browser_main_loop.cc b/content/browser/browser_main_loop.cc
index 330cb631a8b9c582584a90e4a8e980d099b03e23..4e52a51413cdf13748a5525affae192d5b34a72c 100644
--- a/content/browser/browser_main_loop.cc
+++ b/content/browser/browser_main_loop.cc
@@ -1054,7 +1054,7 @@ int BrowserMainLoop::CreateThreads() {
 #else
         if (redirect_nonUInonIO_browser_threads) {
           non_ui_non_io_task_runner_traits
-              .WithPriority(base::TaskPriority::BACKGROUND)
+              .WithPriority(base::TaskPriority::USER_VISIBLE)
               .WithShutdownBehavior(base::TaskShutdownBehavior::BLOCK_SHUTDOWN);
         } else {
           thread_to_start = &file_thread_;