Add XR WPT bug notifications

Adding the line to enable automatic bug filing for when WPTs are
pulled from upstream into the xr folder and are failing.

Change-Id: Idc24b4d610ceaa706c7d7fe12a35a8ff39775b43
Reviewed-on: https://chromium-review.googlesource.com/875249Reviewed-by: David Dorwin <ddorwin@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Commit-Queue: Anna Offenwanger <offenwanger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533066}

third_party/WebKit/LayoutTests/external/wpt/webxr/OWNERS

+# TEAM: xr-dev@chromium.org
+# COMPONENT: Blink>WebVR
+# WPT-NOTIFY: true
 file://third_party/WebKit/Source/modules/xr/OWNERS
\ No newline at end of file