RFR: 8242448: Change HeapRegionManager::guarantee_contiguous_range to be assert_contiguous_range

[Kim Barrett]

> On Apr 14, 2020, at 4:19 AM, Stefan Johansson <stefan.johansson at oracle.com> wrote:
> 
> Hi,
> 
> Please review this follow-up to:
> 8241141: Restructure humongous object allocation in G1
> 
> Webreve: http://cr.openjdk.java.net/~sjohanss/8242448/00/
> JBS: https://bugs.openjdk.java.net/browse/JDK-8242448
> 
> Summary:
> During the review of 8241141 it was mentioned that the guarantee could be switched out to an assert, but the change was pushed without this change. Here is the switch.
> 
> Testing:
> Sanity run in mach5.
> 
> Thanks,
> Stefan

Looks good.