[AspectRatio] Add an OWNERS file for tests

In particular, this opts us into filing bugs for failures.

R=ikilpatrick@chromium.org, mstensho@chromium.org

Change-Id: I3b1eba3dd5b71f8eeb1fbf5fa49bba739fd7d7c4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2489720
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Auto-Submit: Christian Biesinger <cbiesinger@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819317}

third_party/blink/web_tests/external/wpt/css/css-sizing/OWNERS

+# TEAM: layout-dev@chromium.org
+# COMPONENT: Blink>Layout
+# WPT-NOTIFY: true
+cbiesinger@chromium.org