private void ensureOnCreateCalled() {
        if (mNotificationManager != null) return;
        throw new IllegalStateException("TrustedWebActivityService has not been properly "
                + "initialized. Did onCreate() call super.onCreate()?");
    }
See {@link #setVerifiedProvider}, the main difference being that this approach sets the
provider synchronously, so may trigger a disk read.
@hide
customtabs/src/android/support/customtabs/trusted/TrustedWebActivityService.java