RFR: 8205163: ZGC: Keeps finalizable marked PhantomReference referents strongly alive

[Kim Barrett]

> On Jun 18, 2018, at 5:54 AM, Stefan Karlsson <stefan.karlsson at oracle.com> wrote:
> 
> Hi all,
> 
> Please review this patch to fix a bug where PhantomReferences can cause otherwise finalizable objects to become considered as strongly reachable.
> 
> http://cr.openjdk.java.net/~stefank/8205163/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8205163

Looks good.