Use constexpr TaskTraits constructor in chrome.

chrome/browser/chromeos/arc/wallpaper/arc_wallpaper_service.cc

Index: chrome/browser/chromeos/arc/wallpaper/arc_wallpaper_service.cc
diff --git a/chrome/browser/chromeos/arc/wallpaper/arc_wallpaper_service.cc b/chrome/browser/chromeos/arc/wallpaper/arc_wallpaper_service.cc
index bdce3af0c212911a3cc4ebe97b0271258351d6bd..3ae9e9eaf8f53c40e6699b81b2b10bce3494df42 100644
--- a/chrome/browser/chromeos/arc/wallpaper/arc_wallpaper_service.cc
+++ b/chrome/browser/chromeos/arc/wallpaper/arc_wallpaper_service.cc
@@ -221,8 +221,7 @@ void ArcWallpaperService::GetWallpaper(const GetWallpaperCallback& callback) {
   ash::WallpaperController* wc = ash::Shell::Get()->wallpaper_controller();
   gfx::ImageSkia wallpaper = wc->GetWallpaper();
   base::PostTaskWithTraitsAndReplyWithResult(
-      FROM_HERE, base::TaskTraits().MayBlock().WithPriority(
-                     base::TaskPriority::BACKGROUND),
+      FROM_HERE, {base::MayBlock(), base::TaskPriority::BACKGROUND},
       base::Bind(&EncodeImagePng, wallpaper), callback);
 }