RFR (T) 8235685: Shenandoah: Enable leak profiler

[Zhengyu Gu]

Please review this trivial patch that enables JFR leak profiler for 
Shenandoah.

JDK-8235174 enhancement also applies to Shenandoah, we can enable leak 
profiler as well.

Bug: https://bugs.openjdk.java.net/browse/JDK-8235685
Webrev: http://cr.openjdk.java.net/~zgu/JDK-8235685/weberv.00/

Test:
   Use jmc to create JFR recording, eyeball Memory->Live Objects


Thanks,

-Zhengyu