RFR: Upstream merge jdk/jdk -> shenandoah/jdk 2018-08-30

[Zhengyu Gu]

> 
> I included the proposed one-liner fix so that we can run tests.
> 
> - The timers in parallel-cleaning-tasks are gone. We need to rework
> that. Zhengyu?

Yep. Thomas Schatzl wants to overhaul time tracking under single 
framework, did not want this variation to go in.

-Zhengyu

> 
> Testing: tier3_gc_shenandoah (ongoing)
> 
> http://cr.openjdk.java.net/~rkennke/upstream-jdk12-merge-2018-08-30/outgoint.txt
> 
> Ok?
> 
> Roman
>