Enable WPT-NOTIFY in wpt/infrastructure

WPT Import Notification is finally around the corner! And we should of
course fishfood it.

R=foolip

Change-Id: Id05734a4c348b4444c63c4d06aed062d8b60e076
Reviewed-on: https://chromium-review.googlesource.com/830788Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Commit-Queue: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524716}

third_party/WebKit/LayoutTests/external/wpt/infrastructure/OWNERS

 # TEAM: ecosystem-infra@chromium.org
 # COMPONENT: Blink>Infra>Ecosystem
+# WPT-NOTIFY: true
 foolip@chromium.org
 robertma@chromium.org
 smcgruer@chromium.org