RFR(S): 8203921: JFR thread sampling is missing fixes from JDK-8194552

[Markus Gronlund]

Greetings,

Please review the following:

Bug: https://bugs.openjdk.java.net/browse/JDK-8203921 
Webrev: http://cr.openjdk.java.net/~mgronlun/8203921/webrev00/

Summary:

We did an update to the thread sampler logic in order to support proper indexing to the SMR list as part of https://bugs.openjdk.java.net/browse/JDK-8194552 

That fix (already reviewed by rwestberg), was lost unfortunately since the branching sandbox for open source did not incorporate JDK-8194552.
We are seeing similar issues reported now that has already been fixed in JDK-8194552, therefore we need to re-integrate it (minimally customized due to closed vs open).

Thanks
Markus