Use constexpr TaskTraits constructor in chrome.

chrome/browser/download/chrome_download_manager_delegate.cc

Index: chrome/browser/download/chrome_download_manager_delegate.cc
diff --git a/chrome/browser/download/chrome_download_manager_delegate.cc b/chrome/browser/download/chrome_download_manager_delegate.cc
index f1d24f7510b525c5572d949192bf648d9ae90ff3..37c55d6a14feb6b932b00063801f9f4caf33dbd0 100644
--- a/chrome/browser/download/chrome_download_manager_delegate.cc
+++ b/chrome/browser/download/chrome_download_manager_delegate.cc
@@ -729,8 +729,7 @@ void ChromeDownloadManagerDelegate::GetFileMimeType(
     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)