Review request: 7195935: NPG: Some issues with compressed oops

[Stefan Karlsson]

http://cr.openjdk.java.net/~stefank/7195935/webrev/

7195935: NPG: Some issues with compressed oops
Summary: Don't decompress the klass pointer in the G1 pre-barrier code 
when !UseCompressedKlassPointers

The code mimics the behavior in LIRGenerator::do_getClass, including 
using T_OBJECT as the type for src_klass:
LIR_Opr src_klass = new_register(T_OBJECT);

StefanK