RFR: Upstream merge up to d2f118d3f8e7

[Roman Kennke]

This is out-of-order upstream merge up to (but excluding) Zhengyu's
taskqueue stuff, to ease applying to Shenandoah.

I had to resolve some conflicts due to vm_operations renames, and
reshuffling of AdaptiveSizePolicy.

http://cr.openjdk.java.net/~rkennke/upstream-jdk12-merge-2018-12-07/outgoing.txt

Testing (ongoing): hotspot_gc_shenandoah

Ok?

Roman