Request for review: 7132690 InstanceKlass:_reference_type should be u1 type

[Jiangli Zhou]

Hi,

Please review the change for 7132690:

   http://cr.openjdk.java.net/~jiangli/7132690/webrev.00/

It changes InstanceKlass::_reference_type from ReferenceType to u1. The 
ReferenceType is defined as an enum with 6 values 
(src/share/vm/utilities/globalDefinitions.hpp). The change saves 4-byte 
for each class.

Tested with runThese and ute vm.quick.testlist. Ran jprt.

Thanks,

Jiangli