[Spec] Join and bid counts are UTC based (#629)

* [Spec] Join counts are UTC based

* [Spec] Change more places that mention local time to UTC

spec.bs

@@ -265,8 +265,8 @@ This is detectable because it can change the set of fields that are read from th
   1. Set |interestGroup|'s [=interest group/joining origin=] to [=this=]'s
     [=relevant settings object=]'s [=environment/top-level origin=].
   1. If the most recent entry in [=interest group/join counts=] corresponds to
-    the current local day, increment its count. If not, insert a new entry with
-    the time set to the current local day and a count of 1.
+    the current day in UTC, increment its count. If not, insert a new entry with
+    the time set to the current UTC day and a count of 1.
   1. Store |interestGroup| in the browser’s [=interest group set=].
 1. Return |p|.
 
@@ -2266,12 +2266,12 @@ An interest group is a [=struct=] with the following items:
 :: An [=origin=]. The top level page origin from where the interest group was joined.
 : <dfn>join counts</dfn>
 :: A [=list=] containing [=tuples=] of the day and per day join count. The day
-  is calculated based on local time. The join count is a count of the number of
+  is calculated based on UTC time. The join count is a count of the number of
   times {{Navigator/joinAdInterestGroup()}} was called for this interest group on the
   corresponding day.
 : <dfn>bid counts</dfn>
 :: A [=list=] containing [=tuples=] of the day and per day bid count. The day
-  is calculated based on local time. The bid count is a count of the number of
+  is calculated based on UTC time. The bid count is a count of the number of
   times the bid calculated during {{Navigator/runAdAuction()}} was greater than 0.
 : <dfn>previous wins</dfn>
 :: A [=list=] of [=previous wins=].