RFR: Fix mark-preserving in ShenandoahMarkCompact

[Aleksey Shipilev]

On 5/10/19 11:36 AM, Roman Kennke wrote:
> http://cr.openjdk.java.net/~rkennke/fixpreservemark/webrev.00/

Looks good.

Nits:

*) Let's break up long line here:

 249   ShenandoahPrepareForCompactionObjectClosure(PreservedMarks* preserved_marks,
GrowableArray<ShenandoahHeapRegion*>& empty_regions, ShenandoahHeapRegion* to_region) :

*) "heap" is already available at this point:

 835   SharedRestorePreservedMarksTaskExecutor exec(ShenandoahHeap::heap()->workers());


-Aleksey