Fix VR Shell black screen during tests

chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java

Index: chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
index e1e1fb7853516077a6bae0db7de27a2ac3bc20d1..3bb6b02a9d729a5a752585a9e4ea839678e83285 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
@@ -30,6 +30,7 @@ import android.widget.FrameLayout;
 import org.chromium.base.ActivityState;
 import org.chromium.base.ApplicationStatus;
 import org.chromium.base.Log;
+import org.chromium.base.ThreadUtils;
 import org.chromium.base.VisibleForTesting;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
@@ -270,6 +271,7 @@ public class VrShellDelegate implements ApplicationStatus.ActivityStateListener,
         if (sInstance != null) return sInstance;
         VrClassesWrapper wrapper = getVrClassesWrapper();
         if (wrapper == null) return null;
+        ThreadUtils.assertOnUiThread();
         sInstance = new VrShellDelegate(activity, wrapper);
 
         return sInstance;