The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d7fb3a654ec4f0ef7cc56f965c59f71d7c457558

commit d7fb3a654ec4f0ef7cc56f965c59f71d7c457558
Author: Christopher Grant <cjgrant@chromium.org>
Date: Mon Jun 18 21:44:58 2018

VR: Return the floor to being hit-testable

At some point, the floor regressed to be non-hittable.  Mark it as
explicitly hit-testable.

BUG= 853822 
R=tiborg

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:linux_vr;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Ie8ceda269a3e403c4fbf3eeb46709344d1faa90f
Reviewed-on: https://chromium-review.googlesource.com/1104980
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568174}
[modify] https://crrev.com/d7fb3a654ec4f0ef7cc56f965c59f71d7c457558/chrome/browser/vr/ui_scene_creator.cc

This has been verified in Canary.

This bug requires manual review: M68 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: cmasso@(Android), kariahda@(iOS), bhthompson@(ChromeOS), abdulsyed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Do we know why the reticle suddenly no longer hit the floor grid?

AFAICT, the break was quite a while back - looks like Feb 5 at 0338da53dbfa4753a973ce424128d513871144b5, although this is based on a visual inspection.  However, the reticle not hitting the floor isn't obvious.  It manifests as a subtle visual difference in the reticle that you'll only see if you look carefully.

Our UX designer has sharp eyes, and noticed this in a recent review.

It is possible to have a unit test for this, but the tests aren't generally useful - all our UI elements in VR have properties, and the unit tests would amount to "for each element, verify that the properties you set on it equal a hard-coded expected value".  We actually had tests like this previously, but every time we rejig elements, the new configurations would simply have to be copied into the tests to match.

Please make sure to verify the fix in Beta after merging it.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ac275189824f8398aa3ebe5f2236b438dd262e89

commit ac275189824f8398aa3ebe5f2236b438dd262e89
Author: Christopher Grant <cjgrant@chromium.org>
Date: Thu Jun 21 23:42:36 2018

VR: Return the floor to being hit-testable

At some point, the floor regressed to be non-hittable.  Mark it as
explicitly hit-testable.

BUG= 853822 
R=​tiborg

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:linux_vr;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Ie8ceda269a3e403c4fbf3eeb46709344d1faa90f
Reviewed-on: https://chromium-review.googlesource.com/1104980
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#568174}(cherry picked from commit d7fb3a654ec4f0ef7cc56f965c59f71d7c457558)
Reviewed-on: https://chromium-review.googlesource.com/1110901
Reviewed-by: Christopher Grant <cjgrant@chromium.org>
Cr-Commit-Position: refs/branch-heads/3440@{#479}
Cr-Branched-From: 010ddcfda246975d194964ccf20038ebbdec6084-refs/heads/master@{#561733}
[modify] https://crrev.com/ac275189824f8398aa3ebe5f2236b438dd262e89/chrome/browser/vr/ui_scene_creator.cc

Verified in Chrome Beta 68.0.3440.39