RFR (S) 8218879: Keep track of memory accesses originated from Unsafe

[Aleksey Shipilev]

Original RFE:
  https://bugs.openjdk.java.net/browse/JDK-8218879
  https://hg.openjdk.java.net/jdk/jdk/rev/e002408eb0c0

This is needed to get the infrastructure for the follow-up backports (e.g. JDK-8224658). If we don't
do this, parts of this patch would inevitably leak into 11u with those backports. Patch does not
apply cleanly, because context is changed in some places.

11u webrev:
  https://cr.openjdk.java.net/~shade/8218879/webrev.11u.01/

Testing: tier1, tier2.

-- 
Thanks,
-Aleksey