RFR: Merge marked_object_iterate() impls

[Aleksey Shipilev]

On 11/02/2016 03:02 PM, Roman Kennke wrote:
> This merges the two almost identical marked_object_iterate()
> implementations in ShenandoahHeap vs. ShenandoahHeapRegion.
> 
> It introduces two new methods marked_prev_object_iterate() and
> marked_next_object_iterate() which both call the private helper
> marked_object_iterate() with the corresponding mark bitmap and
> top_at_mark_start.
> 
> http://cr.openjdk.java.net/~rkennke/marked_object_iterate/webrev.00/
> 
> Tested by hotspot_gc_test.
> 
> Ok?

Looks good. Thanks a lot, that helps mark prefetch work!

I ran my precious Full GC perf test on release bits with this patch, and
it ran fine without regressions. Also the fastdebug bits do not fail the
tests they used to fail when I was trying to do the same merge.

-Aleksey