RFR (S): 8196602: Change HeapRegionClosure to comply to naming conventions

[Thomas Schatzl]

Hi all,

  can I have reviews for this small change that updates
HeapRegionClosure to comply to the new (actually quite old) Hotspot
naming convention, in particular no camelCase.

CR:
https://bugs.openjdk.java.net/browse/JDK-8196602
Webrev:
http://cr.openjdk.java.net/~tschatzl/8196602/webrev/
Testing:
local compilation, grepping through sources for method names

Thanks,
  Thomas