RFR(S) 8227927: Move ParallelCleaningTask back to G1

[Kim Barrett]

> On Jul 23, 2019, at 3:04 PM, Zhengyu Gu <zgu at redhat.com> wrote:
> 
> ParallelCleaningTask was moved from G1 to shared directory, so Shenandoah can use it. Now, Shenandoah no longer uses it, it can return to G1.
> 
> However, Shenandoah still uses some of sub-tasks defined in shared/parallelCleaning.hpp/cpp, therefore, only ParallelCleaningTask and JVMCICleaningTask are moved to G1.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8227927
> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8227927/webrev.00/index.html
> 
> Test:
>  hotspot_gc (fastdebug and release) on Linux x86_64.
>  Submit tests in progress
> 
> 
> Thanks,
> 
> -Zhengyu

Looks good.