This is not needed for the 90% Review, but should be considered for MVP.

Doug, on my device, I've verified that the problem doesn't happen on 67.  Therefore, this seems to be neither MVP, nor M-67-targeting.  It should be an M-68 issue.  Let me know if you disagree, otherwise, I'll adjust it.

This was caused by https://chromium-review.googlesource.com/c/chromium/src/+/1012989, which fixed a different issue.  That change ensured that if we select an autofill choice, the native UI doesn't steal focus.  The side effect of that was, clicking on "settings" also doesn't steal focus, and the input field keeps focus even when we show the "exit VR" prompt and hide content.

On closer inspection, we show the keyboard simply based on whether we're editing UI input or web input.  If we augment the web input case to be "editing web input and not showing a modal prompt", then we should be good to go.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/958b96f30193d6b21de6cb82de7a882b3848aa2d

commit 958b96f30193d6b21de6cb82de7a882b3848aa2d
Author: Christopher Grant <cjgrant@chromium.org>
Date: Mon Apr 30 16:36:56 2018

VR: Prevent keyboard from showing with exit-VR prompt

If the exit-VR prompt shows while content is editing text, we should
hide the keyboard.  A side effect of this change is that, when the
keyboard disappears, it notifies content that this has happened, and
content loses focus.

In the case of autofill settings, this means that if the user chooses
autofill settings but dismisses the exit-VR prompt to return to their
page, that the input field will no longer be focused for edit (and the
keyboard won't be showing).  In the 2D case, the keyboard is also
hidden, but the cursor is still blinking in the field.  Therefore, VR is
not at parity with 2D, but this feels better than having the keyboard
persist through VR modal dialogs.

BUG= 835483 
R=asimjour

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: I753ec31273e2473a21ea5cd2c2dddf70c962f71a
Reviewed-on: https://chromium-review.googlesource.com/1030873
Reviewed-by: Amirhossein Simjour <asimjour@chromium.org>
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554786}
[modify] https://crrev.com/958b96f30193d6b21de6cb82de7a882b3848aa2d/chrome/browser/android/vr/vr_shell_gl.cc
[modify] https://crrev.com/958b96f30193d6b21de6cb82de7a882b3848aa2d/chrome/browser/vr/elements/content_element_unittest.cc
[modify] https://crrev.com/958b96f30193d6b21de6cb82de7a882b3848aa2d/chrome/browser/vr/elements/keyboard.cc
[modify] https://crrev.com/958b96f30193d6b21de6cb82de7a882b3848aa2d/chrome/browser/vr/ui_scene.cc
[modify] https://crrev.com/958b96f30193d6b21de6cb82de7a882b3848aa2d/chrome/browser/vr/ui_scene.h
[modify] https://crrev.com/958b96f30193d6b21de6cb82de7a882b3848aa2d/chrome/browser/vr/ui_scene_creator.cc

Fix verified in build 67.0.3396.29 beta.  Looks good.