[vr] Close exit prompt when clicking on background

chrome/browser/android/vr_shell/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//chrome/common/features.gni")
 import("//device/vr/features/features.gni")
 import("//testing/test.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
@@ skipping 42 matching lines @@
     "textures/ui_texture.h",
     "textures/url_bar_texture.cc",
     "textures/url_bar_texture.h",
     "ui_browser_interface.h",
     "ui_elements/audio_capture_indicator.cc",
     "ui_elements/audio_capture_indicator.h",
     "ui_elements/button.cc",
     "ui_elements/button.h",
     "ui_elements/exit_prompt.cc",
     "ui_elements/exit_prompt.h",
+    "ui_elements/exit_prompt_backplane.cc",
+    "ui_elements/exit_prompt_backplane.h",
     "ui_elements/exit_warning.cc",
     "ui_elements/exit_warning.h",
     "ui_elements/loading_indicator.cc",
     "ui_elements/loading_indicator.h",
     "ui_elements/permanent_security_warning.cc",
     "ui_elements/permanent_security_warning.h",
     "ui_elements/screen_capture_indicator.cc",
     "ui_elements/screen_capture_indicator.h",
     "ui_elements/screen_dimmer.cc",
     "ui_elements/screen_dimmer.h",
@@ skipping 149 matching lines @@
     "//ui/gl",
   ]
 
   data = [
     "test/data/sample_inline.gltf",
     "test/data/sample_external.gltf",
     "test/data/sample.bin",
     "test/data/sample.glb",
   ]
 }