Use constexpr TaskTraits constructor in chrome.

chrome/browser/download/chrome_download_manager_delegate.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.
 
 #include "chrome/browser/download/chrome_download_manager_delegate.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 711 matching lines @@
   }
 #endif
   callback.Run(content::DOWNLOAD_DANGER_TYPE_NOT_DANGEROUS);
 }
 
 void ChromeDownloadManagerDelegate::GetFileMimeType(
     const base::FilePath& path,
     const GetFileMimeTypeCallback& callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   base::PostTaskWithTraitsAndReplyWithResult(
-      FROM_HERE, base::TaskTraits().MayBlock(), base::Bind(&GetMimeType, path),
-      callback);
+      FROM_HERE, {base::MayBlock()}, base::Bind(&GetMimeType, path), callback);
 }
 
 #if defined(FULL_SAFE_BROWSING)
 void ChromeDownloadManagerDelegate::CheckClientDownloadDone(
     uint32_t download_id,
     DownloadProtectionService::DownloadCheckResult result) {
   DownloadItem* item = download_manager_->GetDownload(download_id);
   if (!item || (item->GetState() != DownloadItem::IN_PROGRESS))
     return;
 
@@ skipping 119 matching lines @@
       path.MatchesExtension(FILE_PATH_LITERAL(".xht")) ||
       path.MatchesExtension(FILE_PATH_LITERAL(".xhtm")) ||
       path.MatchesExtension(FILE_PATH_LITERAL(".xhtml")) ||
       path.MatchesExtension(FILE_PATH_LITERAL(".xsl")) ||
       path.MatchesExtension(FILE_PATH_LITERAL(".xslt"))) {
     return true;
   }
 #endif
   return false;
 }