public Builder setSmallIcon(int icon) {
            mNotification.icon = icon;
            return this;
        }
Set the small icon to use in the notification layouts.  Different classes of devices
may return different sizes.  See the UX guidelines for more information on how to
design these icons.

@param icon A resource ID in the application's package of the drawable to use.
android/android_framework/base/src/main/java/github/tornaco/android/thanos/core/compat/NotificationCompat.java