The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6e94be677fe74b077982fb69c06f566b526949f9

commit 6e94be677fe74b077982fb69c06f566b526949f9
Author: Bill Orr <billorr@chromium.org>
Date: Thu Jan 10 00:49:52 2019

Don't composite WebXR while there is a permission popup

Currently we will render both WebXR and UI, and composite the two.

Instead, WebXR should not be rendered while UI is visible.  This makes
compositing a simple texture copy instead of layering multiple textures,
so improves efficiency and (in the case that resolution is different)
improves quality.

BUG= 912765 

Change-Id: I0baa16411ba621c39305f7eea214f42157d506f9
Reviewed-on: https://chromium-review.googlesource.com/c/1404335
Reviewed-by: Klaus Weidner <klausw@chromium.org>
Commit-Queue: Bill Orr <billorr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621398}
[modify] https://crrev.com/6e94be677fe74b077982fb69c06f566b526949f9/chrome/browser/vr/win/vr_browser_renderer_thread_win.cc
[modify] https://crrev.com/6e94be677fe74b077982fb69c06f566b526949f9/device/vr/windows/compositor_base.cc