RFR (S): 8134631: G1DummyRegionsPerGC fires assert of assert(words <= filler_array_max_size()) failed: too big for a single object

[sangheon.kim]

Hi all,

Can I get some reviews for this change for fixing this assert?

Previous patch(8042668: GC Support for shared heap ranges in CDS) 
limited _filler_array_max_size of G1CollectedHeap to be less than 
humongous threshold.
And this change led this assert as this flag is trying to fill the rest 
of regions with humongous object.

As a fix, I removed the limitation to allow humongous filler and added a 
wrapper function, fill_with_non_humongous_objects().
And replace it with current fill_with_object().

CR:
https://bugs.openjdk.java.net/browse/JDK-8134631
Webrev:
http://cr.openjdk.java.net/~sangheki/8134631/webrev.00/
Test:
JPRT

Thanks,
Sangheon