RFR: JDK-8139293: TestGCEventMixedWithG1ConcurrentMark.java fails after JDK-8134953

[Bengt Rutisson]

Hi everyone,

Could I have a couple of reviews for this fix for a nightly failure?

http://cr.openjdk.java.net/~brutisso/8139293/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8139293

G1 young GCs initiate the concurrent marking cycle. Events sent to 
indicate the concurrent cycle start should use the concurrent thread's 
GC id not the young GC thread's id.

Thanks,
Bengt