Add OpenXR to xr_browser_tests infrastructure and enable tests

This change runs most of the existing OpenVR/WMR tests with
OpenXR by adding OpenXR to the WEBXR_VR_ALL_RUNTIMES* macros.

Remaining tests to add are addressed in:
crbug.com/986637 (input)
crbug.com/986621 (drawing pixels)

Bug: 976434
Change-Id: I6b0a48d37d1380ba50b97b2d97d5b7accb9c495b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1714304
Commit-Queue: Patrick To <patrto@microsoft.com>
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683403}
24 files changed