Remove XRView.viewMatrix

In tests, use XRView.transform.inverse().matrix instead.

This should also fix the issue where XRView.transform was not properly updating on each frame.

Bug: 939615, 944206
Change-Id: Ic28eb75a22ca0f0d230a7f19952df65ce499b405
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1521803
Reviewed-by: Brandon Jones <bajones@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Jacob DeWitt <jacde@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642984}
19 files changed