RFR: 8069016: Add BarrierSet downcast support

[Kim Barrett]

On Feb 27, 2015, at 7:48 PM, Kim Barrett <kim.barrett at oracle.com> wrote:
> 
> On Feb 27, 2015, at 7:15 PM, Sangheon Kim <sangheon.kim at oracle.com> wrote:
>> 
>> Change looks good.
>> But I am not a Reviewer.
> 
> Thanks for your review.  Jon has also reviewed, so now I just need a sponsor.

Except I overlooked Jon’s offer to sponsor.  So I’m all set.

Jon, I’ll send you the export file shortly; I’ve got a couple of trivial merge issues to address (copyright update collisions).