Use constexpr TaskTraits constructor in extensions.

extensions/browser/api/file_handlers/mime_util.cc

Index: extensions/browser/api/file_handlers/mime_util.cc
diff --git a/extensions/browser/api/file_handlers/mime_util.cc b/extensions/browser/api/file_handlers/mime_util.cc
index 4462d3f054e68e20256d3ac78b0927a128445946..bcf2c62f9950e00860cbd93cb88b7aedf2ef23b1 100644
--- a/extensions/browser/api/file_handlers/mime_util.cc
+++ b/extensions/browser/api/file_handlers/mime_util.cc
@@ -74,7 +74,7 @@ void OnGetMimeTypeFromMetadataForNonNativeLocalPathCompleted(
   std::string* const mime_type_from_extension_ptr =
       mime_type_from_extension.get();
   base::PostTaskWithTraitsAndReply(
-      FROM_HERE, base::TaskTraits().MayBlock(),
+      FROM_HERE, {base::MayBlock()},
       base::Bind(base::IgnoreResult(&net::GetMimeTypeFromFile), local_path,
                  mime_type_from_extension_ptr),
       base::Bind(&OnGetMimeTypeFromFileForNonNativeLocalPathCompleted,
@@ -116,7 +116,7 @@ void OnGetMimeTypeFromFileForNativeLocalPathCompleted(
       new std::string(kMimeTypeApplicationOctetStream));
   std::string* const sniffed_mime_type_ptr = sniffed_mime_type.get();
   base::PostTaskWithTraitsAndReply(
-      FROM_HERE, base::TaskTraits().MayBlock(),
+      FROM_HERE, {base::MayBlock()},
       base::Bind(&SniffMimeType, local_path, sniffed_mime_type_ptr),
       base::Bind(&OnSniffMimeTypeForNativeLocalPathCompleted,
                  base::Passed(&sniffed_mime_type), callback));
@@ -148,7 +148,7 @@ void GetMimeTypeForLocalPath(
   std::string* const mime_type_from_extension_ptr =
       mime_type_from_extension.get();
   base::PostTaskWithTraitsAndReply(
-      FROM_HERE, base::TaskTraits().MayBlock(),
+      FROM_HERE, {base::MayBlock()},
       base::Bind(base::IgnoreResult(&net::GetMimeTypeFromFile), local_path,
                  mime_type_from_extension_ptr),
       base::Bind(&OnGetMimeTypeFromFileForNativeLocalPathCompleted, local_path,