RFR: Add stats for partial GC

[Aleksey Shipilev]

On 03/15/2017 05:18 PM, Roman Kennke wrote:
> As $SUBJECT says.
> 
> http://cr.openjdk.java.net/~rkennke/partial-stats/webrev.00/

Bad indent:
  774   _phase_names[partial_gc]                  = "Partial GC";

Otherwise good.

-Aleksey