FHR+Refresh Firefox change in Firefox 35

[Gavin Sharp]

I wanted to just flag a change coming in Firefox 35 to this list -
jjensen and bcolloran are already on the bug, but I figure extra
visibility doesn't hurt.

We landed patches in
https://bugzilla.mozilla.org/show_bug.cgi?id=1063714 and
https://bugzilla.mozilla.org/show_bug.cgi?id=1063710 that changed how
FHR interacts with the "Refresh Firefox" feature.

* FHR data is now persisted across refreshes (it was previously
cleared out when refreshing, i.e. the equivalent of a "new profile")
* the FHR payload now indicates when a refresh occurred

This should hopefully open up the possibility of future analyses of
the effect of refreshes on the other FHR metrics.

Gavin