The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/62a00b455216187db8f37b1e471aca05159f5cc3

commit 62a00b455216187db8f37b1e471aca05159f5cc3
Author: Yash Malik <ymalik@google.com>
Date: Mon Mar 26 19:49:47 2018

VR: Replace legacy exit prompt with the spec-compliant modal prompt.

In this CL, we remove exit_prompt* classes and use prompt* instead.

Bug:  818182 
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;master.tryserver.chromium.linux:linux_vr;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Ia75046518d06b1953db85fa59c240f58dcbb8350
Reviewed-on: https://chromium-review.googlesource.com/978618
Commit-Queue: Yash Malik <ymalik@chromium.org>
Reviewed-by: Christopher Grant <cjgrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545864}
[modify] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/BUILD.gn
[delete] https://crrev.com/a8255fec60ed374e15f7ef5b990bb7fd32bdd53b/chrome/browser/vr/elements/exit_prompt.cc
[delete] https://crrev.com/a8255fec60ed374e15f7ef5b990bb7fd32bdd53b/chrome/browser/vr/elements/exit_prompt.h
[delete] https://crrev.com/a8255fec60ed374e15f7ef5b990bb7fd32bdd53b/chrome/browser/vr/elements/exit_prompt_texture.cc
[delete] https://crrev.com/a8255fec60ed374e15f7ef5b990bb7fd32bdd53b/chrome/browser/vr/elements/exit_prompt_texture.h
[modify] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/elements/prompt.cc
[modify] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/elements/prompt.h
[modify] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/elements/prompt_texture.cc
[modify] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/elements/prompt_texture.h
[rename] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/elements/prompt_unittest.cc
[modify] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/elements/ui_element_name.cc
[modify] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/elements/ui_element_name.h
[modify] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/ui.cc
[modify] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/ui_input_manager_unittest.cc
[modify] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/ui_scene_creator.cc
[modify] https://crrev.com/62a00b455216187db8f37b1e471aca05159f5cc3/chrome/browser/vr/ui_unittest.cc

Verified on build 67.0.3389.0 canary build.  Looks good.
Tests have been updated.