RFR: 8224664: Parallel GC: Use WorkGang (6: PSRefProcTaskProxy)

[Leo Korinth]

Hi,

Here is the sixth patch in a proposed patch series of eight that
removes gcTaskManager and uses the WorkGang abstraction instead.

Here, the new PSRefProcTask is composed of PSRefProcTaskProxy and the
old StealTask (that was partially moved before).

Now both psTasks.* and pcTasks.* are removed.

Enhancement:
   https://bugs.openjdk.java.net/browse/JDK-8224664

Webrev:
 
http://cr.openjdk.java.net/~lkorinth/workgang/0/_8224664-Parallel-GC-Use-WorkGang-6-PSRefProcTaskProxy/
   http://cr.openjdk.java.net/~lkorinth/workgang/0/all/

Testing (on the whole patch series):
   mach5 remote-build-and-test --build-profiles 
linux-x64,linux-x64-debug,macosx-x64,solaris-sparcv9,windows-x64 --test 
open/test/hotspot/jtreg/:hotspot_gc -a -XX:+UseParallelGC
   gc test suite

Thanks,
Leo