RFR: Upstream merge from jdk/jdk12 to jdk-12+28

[Aleksey Shipilev]

On 1/18/19 3:55 PM, Roman Kennke wrote:
> This brings upstream jdk12 into sh/jdk12 up to tag jdk-12+28. Merged
> trivially.
> 
> Testing: hotspot_gc_shenandoah
> 
> http://cr.openjdk.java.net/~rkennke/upstream-jdk12-merge-2019-01-18/outgoing.txt

Yes, good!

-Aleksey