Fix issue with XRBoundedReferenceSpace bounds geometry update

Bounds geometry isn't available until a few seconds after an immersive
session starts for WMR. Blink xr code was only checking if the stage
parameters had changed, but didn't handle the case where the stage
parameters didn't become available until after the session started.

Also updated the E2E test page for bounded reference spaces to properly
call requestReferenceSpace and try creating a bounded reference space
once every second until one becomes available in an immersive session.

Bug: 986867, 986866
Change-Id: I6897269f20ee3814e7f1eeb036c183a85f38d9cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1717453
Commit-Queue: Jacob DeWitt <jacde@chromium.org>
Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681001}
2 files changed