Bug 1605921 [wpt PR 20917] - Update wpt metadata, a=testonly

wpt-pr: 20917 wpt-type: metadata
2020-01-04 03:23:13 +00:00 · 2020-01-04 03:23:13 +00:00 · 74428c7999
--- a/testing/web-platform/meta/native-file-system/dir.ini
+++ b/testing/web-platform/meta/native-file-system/dir.ini
@ -0,0 +1 @@
+leak-threshold: [default:51200]