RFR: JDK-8239081: Shenandoah: Consolidate C1 LRB and native barriers

[Roman Kennke]

>> https://bugs.openjdk.java.net/browse/JDK-8239081
>> Webrev:
>> http://cr.openjdk.java.net/~rkennke/JDK-8239081/webrev.00/
> 
> Only some stylistic nits:
> 
> *) I believe the convention is to name these boolean arguments "is_native"?
> 
> *) C1ShenandoahLoadReferenceBarrierCodeGenClosure::_native should probably be const?

Right, good points! Both fixed here:

http://cr.openjdk.java.net/~rkennke/JDK-8239081/webrev.01/

Good now?

Thanks for reviewing!
Roman