[11u] RFR (XS) 8240751: Shenandoah: fold ShenandoahTracer definition

[Roman Kennke]

> Original RFE:
>    https://bugs.openjdk.java.net/browse/JDK-8240751
>    https://git.openjdk.java.net/jdk/commit/382b8fed
> 
> The context have changed, so patch does not apply cleanly. The patch 
> itself is rather trivial.
> 
> 11u webrev:
>    https://cr.openjdk.java.net/~shade/8240751/webrev.11u.01/
> 
> Testing: Linux x86_64 {fastdebug,release} builds

Looks good, thank you!

Roman