Merge upstream to jdk-12+31

[Aleksey Shipilev]

On 2/11/19 2:52 PM, Roman Kennke wrote:
>> Looks okay. At some point in the future, we would need to switch to jdk-updates/jdk12u. I have
>> backported quite a few Shenandoah fixes there already, and those fixes are not present in jdk/jdk12.
> 
> Right. I assume jdk-12+31 will land in jdk-updates/jdk12u? Otherwise
> this change would make a little mess.

I think jdk/jdk12 would be merged to jdk-updates/jdk12u before jdk/jdk12 ceases to exist, bringing
all changes and tags to update release. IIRC, that is what happened with jdk/jdk11.

-Aleksey