RFR: 8211446: Replace oop_pc_follow_contents with oop_iterate and closure

[Leo Korinth]

Hi!

This is the is the second enhancement in a series of three to remove 
Parallel GC specific behaviour from shared code. I will post all three 
enhancements to the mailing list.

For a description on what is changed see my earlier "RFR: 8201436: 
Replace oop_ps_push_contents with oop_iterate and closure"

Enhancement:
https://bugs.openjdk.java.net/browse/JDK-8211446

Webrev:
http://cr.openjdk.java.net/~lkorinth/8211446/00/

Testing:
- all patches build on linux after the latest rebase.
- mach5 (linux, windows and mac) tier1,tier2,tier3,tier4,tier5 has 
passed with all three patches applied
- aurora tests have been run and seem to indicate no change in general 
on this webrev in the patch series.

Thanks, Leo