Would be ideal to have this solved prior to M68, but that may be a stretch depending on how complicated the fix end up being.

I wonder if this is related to 842653

This is likely due to old code that draws the background from 6 quads, instead of just filling the full screen (which we now have an element for).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/01c1a77e00773fe4985ae7ddc5d6843c6f70e8b7

commit 01c1a77e00773fe4985ae7ddc5d6843c6f70e8b7
Author: Christopher Grant <cjgrant@chromium.org>
Date: Tue May 22 21:28:18 2018

VR: Draw the solid color background using full-screen rect

The old box of quads shows seams on high-res displays.  We used this
approach because there was no full-screen UI element.

BUG= 844488 

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_vr
Change-Id: I91d7921b192cf0f963593001af5ad92211d7e6d8
Reviewed-on: https://chromium-review.googlesource.com/1069428
Reviewed-by: Biao She <bshe@chromium.org>
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560782}
[modify] https://crrev.com/01c1a77e00773fe4985ae7ddc5d6843c6f70e8b7/chrome/browser/vr/elements/ui_element_name.cc
[modify] https://crrev.com/01c1a77e00773fe4985ae7ddc5d6843c6f70e8b7/chrome/browser/vr/elements/ui_element_name.h
[modify] https://crrev.com/01c1a77e00773fe4985ae7ddc5d6843c6f70e8b7/chrome/browser/vr/test/ui_test.cc
[modify] https://crrev.com/01c1a77e00773fe4985ae7ddc5d6843c6f70e8b7/chrome/browser/vr/ui_scene_creator.cc
[modify] https://crrev.com/01c1a77e00773fe4985ae7ddc5d6843c6f70e8b7/chrome/browser/vr/ui_unittest.cc