Use constexpr TaskTraits constructor in chrome.

chrome/browser/chromeos/app_mode/startup_app_launcher.cc

Index: chrome/browser/chromeos/app_mode/startup_app_launcher.cc
diff --git a/chrome/browser/chromeos/app_mode/startup_app_launcher.cc b/chrome/browser/chromeos/app_mode/startup_app_launcher.cc
index 8ec0a15b9a191bd3ff8fee97c98a9dde9ba317af..ea235737add8ccea0a900a2f199f9e0644922ff5 100644
--- a/chrome/browser/chromeos/app_mode/startup_app_launcher.cc
+++ b/chrome/browser/chromeos/app_mode/startup_app_launcher.cc
@@ -119,8 +119,7 @@ void StartupAppLauncher::StartLoadingOAuthFile() {
 
   KioskOAuthParams* auth_params = new KioskOAuthParams();
   base::PostTaskWithTraitsAndReply(
-      FROM_HERE, base::TaskTraits().MayBlock().WithPriority(
-                     base::TaskPriority::BACKGROUND),
+      FROM_HERE, {base::MayBlock(), base::TaskPriority::BACKGROUND},
       base::Bind(&StartupAppLauncher::LoadOAuthFileAsync, auth_params),
       base::Bind(&StartupAppLauncher::OnOAuthFileLoaded, AsWeakPtr(),
                  base::Owned(auth_params)));