RFR: Introduce assert_in_correct_region to verify object is in correct region

[Roman Kennke]

Am 11.04.2018 um 19:52 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/assert-correct-region/webrev.01/
> 
> RTM folks report there is an assertion failure on in their systems, seems like humongous region was
> reclaimed too soon. Unfortunately, the assert there is not very informative, and we should make it a
> bit better.
> 
> Testing: hotspot_gc_shenandoah {fastdebug|release}
> 
> Thanks,
> -Aleksey
> 

Ok, makes sense! Looks good!

Roman