[RFR] 8061715: gc/g1/TestShrinkAuxiliaryData15.java fails with java.lang.RuntimeException: heap decommit failed - after > before

[Andrey Zakharov]

Hello.
Summary: test for auxiliary data in G1 fails as they cannot precisely 
measure this aux data size.
I've added whitebox method to get this size.
I've on little question about placement of helper method 
"sum_memory_usage", which currently placed in
gc_implementation/g1/heapRegionManager.hpp but it doesn't logically 
related to HeapManager itself.
If you can advice me where its best place it will be wonderful.

webrev:
http://cr.openjdk.java.net/~azakharov/8061715/webrev/
bug:
JDK-8061715 gc/g1/TestShrinkAuxiliaryData15.java fails with 
java.lang.RuntimeException: heap decommit failed - after > before

Testing done in Stockholm's JPRT (2015-02-12-112315.azakharov.hs-gc) all 
is fine.

Thanks.