hg: shenandoah/jdk: Precleaning should use GC workers to do actual work

[shade at redhat.com]

Changeset: 6010dbce31d3
Author:    shade
Date:      2018-10-03 13:07 +0200
URL:       http://hg.openjdk.java.net/shenandoah/jdk/rev/6010dbce31d3

Precleaning should use GC workers to do actual work

! src/hotspot/share/gc/shenandoah/shenandoahConcurrentMark.cpp
! src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp
! src/hotspot/share/gc/shenandoah/shenandoahTraversalGC.cpp
! src/hotspot/share/gc/shenandoah/shenandoahWorkGroup.cpp
! src/hotspot/share/gc/shenandoah/shenandoahWorkGroup.hpp
! src/hotspot/share/gc/shenandoah/shenandoahWorkerPolicy.cpp