RFR: Backport string dedup to jdk8u

[Aleksey Shipilev]

On 05/18/2018 05:31 PM, Zhengyu Gu wrote:
> Backport is pretty straightforward from jdk9. It took longer than expected, cause I fell into
> Atomic::add(jlong) trap again :-(
> 
> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/8u-strdedup/webrev.00/

Yup, looks straightforward. Thanks!

Tests timeout for me though (sh/jdk8u is slower), so I needed to apply this:
  http://cr.openjdk.java.net/~shade/shenandoah/strdedup-8-timeouts.patch

-Aleksey