RFR: Make statistics gathering span more operations

[Roman Kennke]

Am 30.05.2017 um 12:55 schrieb Aleksey Shipilev:
> We seem to be doing some work in shadows, without GC stats recording it. I
> scanned the code for all our VM ops, and this change moves the phase_(start|end)
> statements around to capture the timings better:
>   http://cr.openjdk.java.net/~shade/shenandoah/stats-closer/webrev.01/
>
> Testing: hotspot_gc_shenandoah

Ok.
clear-matrix probably warrants its own measurement? Up to you.

Roman