@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
    RequestManagerFragment getRequestManagerFragment(final android.app.FragmentManager fm) {
        RequestManagerFragment current = (RequestManagerFragment) fm.findFragmentByTag(FRAGMENT_TAG);
        if (current == null) {
            current = pendingRequestManagerFragments.get(fm);
            if (current == null) {
                current = new RequestManagerFragment();
                pendingRequestManagerFragments.put(fm, current);
                fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
                handler.obtainMessage(ID_REMOVE_FRAGMENT_MANAGER, fm).sendToTarget();
            }
        }
        return current;
    }
Retrieves and returns the RequestManagerRetriever singleton.
core/src/main/java/com/bumptech/glide/manager/RequestManagerRetriever.java