Add sample page that leverages prototype Anchor APIs

The phone-ar-plane-detection-anchors.html is mostly a copy-paste of
phone-ar-plane-detection.html with minor changes to leverage anchors
API.

Change-Id: I96a8a02e67dade63030d425dc2c3e58088bf253e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1796524
Commit-Queue: Piotr Bialecki <bialpio@chromium.org>
Reviewed-by: Klaus Weidner <klausw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695783}
2 files changed