Use constexpr TaskTraits constructor in chrome.

chrome/browser/ui/webui/print_preview/printer_backend_proxy_chromeos.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/ui/webui/print_preview/printer_backend_proxy.h"
 
 #include <memory>
 #include <vector>
 
 #include "base/bind_helpers.h"
@@ skipping 48 matching lines @@
   }
 }
 
 void FetchCapabilities(std::unique_ptr<chromeos::Printer> printer,
                        const PrinterSetupCallback& cb) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
   PrinterBasicInfo basic_info = ToBasicInfo(*printer);
 
   base::PostTaskWithTraitsAndReplyWithResult(
-      FROM_HERE,
-      base::TaskTraits().MayBlock().WithPriority(
-          base::TaskPriority::BACKGROUND),
+      FROM_HERE, {base::MayBlock(), base::TaskPriority::BACKGROUND},
       base::Bind(&GetSettingsOnBlockingPool, printer->id(), basic_info), cb);
 }
 
 void HandlePrinterSetup(std::unique_ptr<chromeos::Printer> printer,
                         const PrinterSetupCallback& cb,
                         chromeos::PrinterSetupResult result) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
   switch (result) {
     case chromeos::PrinterSetupResult::SUCCESS:
@@ skipping 93 matching lines @@
 };
 
 }  // namespace
 
 std::unique_ptr<PrinterBackendProxy> PrinterBackendProxy::Create(
     Profile* profile) {
   return base::MakeUnique<PrinterBackendProxyChromeos>(profile);
 }
 
 }  // namespace printing