RFR(S): ShenandoahGCSession used wrong timer for full GC

[Aleksey Shipilev]

On 06/22/2017 09:07 PM, Zhengyu Gu wrote:
> ShenandoahGCSession should use STW timer instead of concurrent timer during full
> GC.
> 
> Webrev:
> http://cr.openjdk.java.net/~zgu/shenandoah/gcsession_timer/webrev.00/index.html

I think enum is redundant, can just say:

  ShenandoahGCSession session(/* is_full_gc = */ true);

Otherwise looks fine.

-Aleksey