RFR (T) 8222977: Fix shenandoah broken with JDK-8222811

[coleen.phillimore at oracle.com]

open webrev at http://cr.openjdk.java.net/~coleenp/2019/8222977.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8222977

I just found this.  Please review before Aleksey finds it. Shendandoah 
build in progress.

Thanks,
Coleen