@Override
        public Bundle areNotificationsEnabled(Bundle bundle) {
            checkCaller();

            NotificationsEnabledArgs args = NotificationsEnabledArgs.fromBundle(bundle);
            boolean result =
                    TrustedWebActivityService.this.areNotificationsEnabled(args.channelName);

            return new ResultArgs(result).toBundle();
        }
Used as a return value of {@link #getSmallIconId} when the icon is not provided.
customtabs/src/android/support/customtabs/trusted/TrustedWebActivityService.java