8135260: Split G1CollectorPolicy::finalize_cset into two parts

[Erik Helin]

Hi all,

this tiny patch splits the rather large method
G1CollectorPolicy::finalize_cset into two parts:
- G1CollectorPolicy::finalize_young_cset_part
- G1CollectorPolicy::finalize_old_cset_part

Webrev:
http://cr.openjdk.java.net/~ehelin/8135260/webrev.00/

Enhancement:
https://bugs.openjdk.java.net/browse/JDK-8135260

Testing:
- JPRT

Thanks,
Erik