[vr] Close exit prompt when clicking on background

chrome/browser/android/vr_shell/ui_scene_manager.h

Index: chrome/browser/android/vr_shell/ui_scene_manager.h
diff --git a/chrome/browser/android/vr_shell/ui_scene_manager.h b/chrome/browser/android/vr_shell/ui_scene_manager.h
index c762d1d81f031d52b0b5c3e5b1bee0c3ba51b49f..e7c2658fcf36d4a52bf6cc94810a513ea2ff9e7b 100644
--- a/chrome/browser/android/vr_shell/ui_scene_manager.h
+++ b/chrome/browser/android/vr_shell/ui_scene_manager.h
@@ -54,6 +54,7 @@ class UiSceneManager {
 
  private:
   FRIEND_TEST_ALL_PREFIXES(UiSceneManagerTest, UiUpdatesExitPrompt);
+  FRIEND_TEST_ALL_PREFIXES(UiSceneManagerTest, BackplaneClickClosesExitPrompt);
 
   void CreateScreenDimmer();
   void CreateSecurityWarnings();
@@ -66,8 +67,10 @@ class UiSceneManager {
   void ConfigureScene();
   void ConfigureSecurityWarnings();
   void UpdateBackgroundColor();
+  void CloseExitPrompt();
   void OnSecurityWarningTimer();
   void OnBackButtonClicked();
+  void OnBackplaneClicked();
   void OnSecurityIconClicked();
   void OnExitPromptPrimaryButtonClicked();
   void OnExitPromptSecondaryButtonClicked();