RFR (S): 8228388: Add information about dirty/skipped card for Merge HCC in G1 log

[Kim Barrett]

> On Jul 18, 2019, at 12:27 PM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi all,
> 
>  can I have reviews for this small change that adds information about
> how many cards were flushed/used from the HCC during GC?
> 
> This removes one annoyance that otherwise the amount of scanned cards
> in the scan heap roots phase looks to be larger than the sum of cards
> from the remembered sets and log buffers at times.
> 
> Also I need that value for JDK-8227739 (so far).
> 
> I added a small test case that checks whether G1 survives a GC without
> HCC enabled - there is no such test yet, but seemed appropriate.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8228388
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8228388/webrev/
> Testing:
> hs-tier1, local gc/g1 run, new test, eyeballing log message output
> 
> Thanks,
>  Thomas

Looks good.