Use constexpr TaskTraits constructor in chrome.

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

 // Copyright 2016 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/chromeos/arc/wallpaper/arc_wallpaper_service.h"
 
 #include <stdlib.h>
 
 #include <deque>
 
@@ skipping 203 matching lines @@
   const PrimaryAccount& account = GetPrimaryAccount();
   chromeos::WallpaperManager::Get()->SetDefaultWallpaper(account.id,
                                                          account.is_active);
 }
 
 void ArcWallpaperService::GetWallpaper(const GetWallpaperCallback& callback) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   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);
 }
 
 void ArcWallpaperService::OnWallpaperDataChanged() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
   auto* const wallpaper_instance = ARC_GET_INSTANCE_FOR_METHOD(
       arc_bridge_service()->wallpaper(), OnWallpaperChanged);
   const ash::WallpaperController* const wc = GetWallpaperController();
   const int32_t android_id =
       wc ? android_id_store_->Pop(wc->GetWallpaperOriginalImageId()) : -1;
   if (!wallpaper_instance)
     return;
   wallpaper_instance->OnWallpaperChanged(android_id);
 }
 
 }  // namespace arc