RFR: 8178836: Improve PtrQueue index abstraction

[Kim Barrett]

> On Apr 21, 2017, at 7:00 PM, Kim Barrett <kim.barrett at oracle.com> wrote:
>> Minor nits:
>> 
>> *) On first scan, "limit" reads as the loop variable, because it is the only
>> initialization in init block. Move it out?
>> 
>> 161   for (size_t limit = buffer_size(); i < limit; ++i) {
> 
> OK.

Updated webrev:
full: http://cr.openjdk.java.net/~kbarrett/8178836/hotspot.01/
incr: http://cr.openjdk.java.net/~kbarrett/8178836/hotspot.01.inc/