@Override
    public void onLowMemory() {
        super.onLowMemory();
        // If an activity is re-created, onLowMemory may be called before a manager is ever set.
        // See #329.
        if (requestManager != null) {
            requestManager.onLowMemory();
        }
    }
Returns true if the fragment is a descendant of our parent.
core/src/main/java/com/bumptech/glide/manager/SupportRequestManagerFragment.java