Fix phone-ar.html WebXR sample

Change-Id: I9b9e2291b56981fe11a5b3ed3033aefbdd2c1779
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1506461
Auto-Submit: Piotr Bialecki <bialpio@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Brandon Jones <bajones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638273}
1 file changed