RFR: 8058298: Separate heap region iterator claim values from the data structures iterated over

[Marcus Larsson]

Hi,

I would like reviews for the following refactorization to separate the 
heap region claiming from the actual heap region data structure. This 
allows concurrent tasks to claim heap regions independent of each other.

The patch adds a HeapRegionClaimer that should be used for parallel 
iteration over heap regions, and will handle the claims for a certain 
task. The previous claim field and its associated functions in 
HeapRegion is removed.

Webrev:
http://cr.openjdk.java.net/~brutisso/webrev-8058298/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8058298

Testing:
jprt
local UTE vm.gc.testlist
SPECjbb2013

Thanks,
Marcus