[8u60] RFR backport of 8067655: Clean up G1 remembered set oop iteration

[Thomas Schatzl]

Hi all,

  can I have reviews for the backport of "8067655: Clean up G1
remembered set oop iteration" for 8u60?

It did only apply with minor changes, so I need re-reviews. The problems
are
- some guarantee that is still in jdk8u in G1RemSet::G1RemSet(), but has
been removed in jdk9
- in jdk9, FREE_C_HEAP_ARRAY does not need the type specifier ("mtGC")
any more
- CountNonCleanMemRegionClosure moved in jdk9

Note that this change is based on "8069273: Decrease Hot Card Cache Lock
contention" which is also out for review, and "8069760: When iterating
over a card, G1 often iterates over much more..." which applied cleanly
(hence no RFR for that one).

Full 8u60 changeset:
http://cr.openjdk.java.net/~tschatzl/8067655-8u60/webrev.8u60/
Diff changest:
http://cr.openjdk.java.net/~tschatzl/8067655-8u60/webrev.8u60-fix/

CR:
https://bugs.openjdk.java.net/browse/JDK-8067655

Original change:
http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/6aa9ea790814

Testing: jprt

Thanks,
  Thomas