RFR: Hook up GCLABs to Elastic LAB support

[Roman Kennke]

Am 13.07.2018 um 16:16 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/elastic-gclabs/webrev.01/
> 
> Eyeballed Visualizer on some workloads, and noticed that after we allowed GCLABs to take the entire
> region (as the side effect for elastic TLABs to have max_tlab_size = heap_region_size), they started
> to fragment the heap aggressively. Thus we need to resolve the TODO item to hook them up to elastic
> machinery right away.
> 
> Testing: tier3_gc_shenandoah, benchmarks
> 
> Thanks,
> -Aleksey
> 

Looks good, thank you!

Roman