RFR: 8224663: Parallel GC: Use WorkGang (5: ScavengeRootsTask)

[Leo Korinth]

Hi!

Here is the latest fixup (fixup3) rebased on latest.
http://cr.openjdk.java.net/~lkorinth/workgang/3/fixups/

I will push it like this:
http://cr.openjdk.java.net/~lkorinth/workgang/3/fixups_collapsed/

All changes collapsed:
http://cr.openjdk.java.net/~lkorinth/workgang/3/all_collapsed/

I did fix JVMCI include order in:
src/hotspot/share/gc/parallel/psParallelCompact.cpp
but the include was rebased away in:
src/hotspot/share/gc/parallel/psScavenge.cpp

all 8 collapsed changes do compile and pass the :hotspot_gc with 
-XX:+UseParallelGC

If you are okay with this I will run more testing on all changes, again 
checking performance and running slowdebugs etc.

I also added StefanK as reviewer. He has suggested many improvements 
before the first public review.

Are you okay with all the 8 commits?

Thanks,
Leo