RFR: 8199739: Use HeapAccess when loading oops from static fields in javaClasses.cpp

[Stefan Karlsson]

Hi all,

Please review this patch to use HeapAccess<>::oop_load instead of 
oopDesc::load_decode_heap_oop when loading oops from static fields in 
javaClasses.cpp:

http://cr.openjdk.java.net/~stefank/8199739/webrev.01/
https://bugs.openjdk.java.net/browse/JDK-8199739

It's necessary to use HeapAccess<>::oop_load to inject load barriers for 
GCs that need them.

Thanks,
StefanK