Support XRBoundedReferenceSpace

If the backend indicates supports, will allow XRBoundedReferenceSpaces to be
created. The bounds will be the four corners of what was previously exposed
to WebVR as the play area width and depth.

Bug: 922175
Change-Id: Icf5ea3e497130a47a3db5021e76e06da990df8bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1539819
Commit-Queue: Brandon Jones <bajones@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Klaus Weidner <klausw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#651422}
27 files changed