[Patch] Fix missing shenandoah entry in GCNameHelper::to_string

[Joshua Matsuoka]

Hi,

A case for Shenandoah was missing in GCNameHelper's to_string method. The
result of this was when trying to use Flight Recorder, it would call this
method as part of writing the GC Name then fall through to the default case
and end up with a ShouldNotReachHere.

The attached patch adds the missing case and resolves the issue.

Thoughts?

Cheers,

- Josh
-------------- next part --------------
A non-text attachment was scrubbed...
Name: fix_jfr.patch
Type: text/x-patch
Size: 432 bytes
Desc: not available
URL: <http://mail.openjdk.java.net/pipermail/shenandoah-dev/attachments/20180620/a3a80e0d/fix_jfr.patch>