8189360: JvmtiExport::weak_oops_do is called for all JNIHandleBlock instances

[Stefan Karlsson]

Hi all,

Please review this patch to move the call of the static 
JvmtiExport::weak_oops_do out of the JNIHandleBlock::weak_oops_do member 
function into the new WeakProcessor.

Today, this isn't causing any bugs because there's only one instance of 
JNIHandleBlock, the _weak_global_handles. However, in prototypes with 
more than one JNIHandleBlock, this results in multiple calls to 
JvmtiExport::weak_oops_do.

http://cr.openjdk.java.net/~stefank/8189360/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8189360

This patch builds upon the patch in:
http://mail.openjdk.java.net/pipermail/hotspot-dev/2017-October/028684.html

Tested with JPRT.

Thanks,
StefanK