Adding OWNERS file to new filter-effects folder.

Change-Id: Icf9fd7a9ebd1f9753ef2e26d74bb91bd9598650f
Reviewed-on: https://chromium-review.googlesource.com/c/1330697Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607064}

third_party/WebKit/LayoutTests/external/wpt/css/filter-effects/OWNERS

+# TEAM: paint-dev@chromium.org
+# COMPONENT: Blink>Paint
+# WPT-NOTIFY: true