Move constructable stylesheets layout test to WPT

We're shipping constructable stylesheets soon, so moving the layout
test to WPT now.

Draft spec: https://wicg.github.io/construct-stylesheets/index.html

Bug: 807560
Change-Id: I37b45b6bbb1b17da51fbc41fbac5f11caabc5070
Reviewed-on: https://chromium-review.googlesource.com/c/1375296
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616226}
2 files changed