RFR: Consolidate oop iterators

[Aleksey Shipilev]

On 02/06/2017 10:15 PM, Roman Kennke wrote:
> http://cr.openjdk.java.net/~rkennke/consolidate-closures/webrev.00/

Looks good.

 *) I think we can ditch ShenandoahMarkRefsSuperClosure now, and make all
subclasses extend MetadataAwareOopClosure directly.

 *) If we migrate the last remaining use of SCM::mark_and_push in
ShenandoahSATBBufferClosure, we can then merge mark_in_push into
mark_through_ref, right?

Thanks,
-Aleksey