[15] RFR 8243323: Shenandoah: Recycle immediate garbage before concurrent class unloading

[Zhengyu Gu]

Please review this patch that allows Shenandoah to recycle immediate 
garbage before performing concurrent class unloading. Please see bug for 
details.


Bug: https://bugs.openjdk.java.net/browse/JDK-8243323
Webrev: http://cr.openjdk.java.net/~zgu/JDK-8243323/webrev.00/index.html

Test:
   hotspot_gc_shenandoah
   tier1 with ShenandoahGC

Thanks,

-Zhengyu