Protect GrantCredentialsPermissionActivity against overlay. am: f45dcfe1f5 am: 3f47c701f1 am: 765788de9a

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/13029378

Change-Id: Idaef7cd6bbcee766a7e25c301248daa24a04bd2b