AR sample: implement synchronous hittest in JS using detected planes

This adds one more AR sample page that relies on incubated plane
detection API to implement synchronous hit test purely in JavaScript.

Change-Id: I7d98fb5f656eb4068facf83b4de8ac9a7b49f334
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1597276
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Piotr Bialecki <bialpio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658283}
9 files changed