This is being fixed as part of a larger visibility refactoring

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b

commit 27d7cd5c316f089d529a4edbd9db07b4e21c2b5b
Author: Christopher Grant <cjgrant@chromium.org>
Date: Wed May 02 21:00:03 2018

VR: Make modal prompts a non-opaque UI mode

Having a dedicated mode for prompts should make visibility of other
elements simpler when prompts are active.  To make this work:

- Simplify voice search, content and omnibox's visibility gating logic
- Fix voice search metrics reporting
- Add vollick@'s  sequence object to introduce an alternative to transient
  elements
- Removed illegal visibility bindings (ancestor bound to descendant) and
  related hacky workarounds.

BUG= 829880 

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: Ic0f6c7546797b956eda02e50fd9384149a3612c6
Reviewed-on: https://chromium-review.googlesource.com/1031209
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Reviewed-by: Ian Vollick <vollick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555511}
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/android/vr/vr_shell.cc
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/BUILD.gn
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/elements/scaled_depth_adjuster.cc
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/elements/ui_element.cc
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/elements/ui_element.h
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/elements/ui_element_name.cc
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/elements/ui_element_name.h
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/model/model.cc
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/model/model.h
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/model/ui_mode.h
[add] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/sequence.cc
[add] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/sequence.h
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/testapp/vr_test_context.cc
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/ui.cc
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/ui.h
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/ui_scene.cc
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/ui_scene.h
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/ui_scene_constants.h
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/ui_scene_creator.cc
[modify] https://crrev.com/27d7cd5c316f089d529a4edbd9db07b4e21c2b5b/chrome/browser/vr/ui_unittest.cc