RFR: Cleanup buffered queue handling for Shenandoah

[Zhengyu Gu]

Looks good.

Thanks,

-Zhengyu

On 09/18/2018 11:10 AM, Aleksey Shipilev wrote:
> http://cr.openjdk.java.net/~shade/shenandoah/concmark-queue-cleanup/webrev.01/
> 
> This cleans up the handling for our marking queues: encapsulates most of the code in the queue code
> itself, and moves our new implementation to our own file, reducing upstream exposure. We can move
> new implementations back after upstreaming.
> 
> Testing: tier3_gc_shenandoah
> 
> Thanks,
> -Aleksey
>