VrShell: Add test for fullscreen transitions.

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 4eae5b1a586bb6dd5096bc1cdeca4e7c7c69c75a..cf3ec17dd6445f78b81d16837b9b3e15047701c2 100644
--- a/chrome/browser/android/vr_shell/ui_scene_manager.h
+++ b/chrome/browser/android/vr_shell/ui_scene_manager.h
@@ -5,6 +5,7 @@
 #ifndef CHROME_BROWSER_ANDROID_VR_SHELL_UI_SCENE_MANAGER_H_
 #define CHROME_BROWSER_ANDROID_VR_SHELL_UI_SCENE_MANAGER_H_
 
+#include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/timer/timer.h"
@@ -75,6 +76,8 @@ class UiSceneManager {
 
   base::WeakPtrFactory<UiSceneManager> weak_ptr_factory_;
 
+  FRIEND_TEST_ALL_PREFIXES(UiSceneManagerTest, UiUpdatesForFullscreen);
+
   DISALLOW_COPY_AND_ASSIGN(UiSceneManager);
 };