Revert "Report first_paint in milliseconds"
Revert "Report first_paint in milliseconds"

It turns out that this patch reports 0 as the first_paint time on page
reloads.  Better to report in seconds.microseconds and convert
server-side.

This reverts commit aabcbe1360a2f779d23dad31c75dbe7d1c720001.

FredXue/boomerang,forcedotcom/kylie,sdgdsffdsfff/boomerang,FredXue/boomerang,levexis/boomerang,forcedotcom/kylie,sdgdsffdsfff/boomerang,lognormal/boomerang,lognormal/boomerang,levexis/boomerang