GitLab

Detached the xr test folder from the vr test folder by creating its own
set of helper classes. Converted all tests to promise tests where it
made sense. As much as possible detached chrome specific code for when
we convert tests to WPTs.

Bug: 777567
Change-Id: I90e7800cbf86b09f72937033e4a840d1f5719b61
Reviewed-on: https://chromium-review.googlesource.com/889652
Commit-Queue: Anna Offenwanger <offenwanger@chromium.org>
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532987}