RFR: 8134806: Clean up write_ref_field_work

[Tom Benson]

Looks good to me -
Tom

On 9/1/2015 10:59 AM, Kim Barrett wrote:
> Please review this small cleanup of BarrierSet::write_ref_field_work.
> This change
>
> - Removes an unnecessary pure virtual declaration.
>
> - Removes mostly unused default argument values, adding an explicit
> argument to one caller.
>
> - Changes an unnecessarily public declaration to protected.
>
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8134806
>
> Webrev:
> http://cr.openjdk.java.net/~kbarrett/8134806/webrev.00/
>
> Testing:
> jprt
>