Use constexpr TaskTraits constructor in chrome.

chrome/browser/printing/cloud_print/test/cloud_print_proxy_process_browsertest.cc

 // Copyright (c) 2012 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.
 
 // Create a service process that uses a Mock to respond to the browser in order
 // to test launching the browser using the cloud print policy check command
 // line switch.
 
 #include <stdint.h>
 
@@ skipping 465 matching lines @@
   return std::move(spawn_result.process);
 }
 
 void CloudPrintProxyPolicyStartupTest::WaitForConnect() {
   observer_.Wait();
   EXPECT_TRUE(CheckServiceProcessReady());
   EXPECT_TRUE(base::ThreadTaskRunnerHandle::Get().get());
 
   mojo::MessagePipe pipe;
   base::PostTaskWithTraits(
-      FROM_HERE,
-      base::TaskTraits().MayBlock().WithPriority(
-          base::TaskPriority::BACKGROUND),
+      FROM_HERE, {base::MayBlock(), base::TaskPriority::BACKGROUND},
       base::BindOnce(&ConnectAsync, base::Passed(&pipe.handle1),
                      GetServiceProcessChannel()));
   ServiceProcessControl::GetInstance()->SetChannel(
       IPC::ChannelProxy::Create(IPC::ChannelMojo::CreateClientFactory(
                                     std::move(pipe.handle0), IOTaskRunner()),
                                 this, IOTaskRunner()));
 }
 
 bool CloudPrintProxyPolicyStartupTest::Send(IPC::Message* message) {
   return ServiceProcessControl::GetInstance()->Send(message);
@@ skipping 40 matching lines @@
   // constructed.
   chrome::TestingIOThreadState testing_io_thread_state;
 
   base::Process process =
       Launch("CloudPrintMockService_StartEnabledWaitForQuit");
   WaitForConnect();
   ShutdownAndWaitForExitWithTimeout(std::move(process));
   ServiceProcessControl::GetInstance()->Disconnect();
   content::RunAllPendingInMessageLoop();
 }