RFR(XS) Eliminating _num_regions variable in ShenandoahHeap

[Aleksey Shipilev]

On 06/28/2017 03:26 PM, Zhengyu Gu wrote:
> Eliminate dual states which might result out-of-sync problem.
> and use _ordered_regions->active_regions() solely.
> 
> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/heap_regions_count/webrev.00/

Good! Minor things:

 *) Write something here?

 190   assert(_ordered_regions->active_regions() == num_regions, "");

 *) Invert this to ">="?

 107   if (!(index < num_regions())) {


Thanks,
-Aleksey