Night Light: Timezone changes result in recalculation of sunset/sunrise times

On timezone changes, request a new geoposition and push it to the
NightLightController in ash in order to recalculate the sunset/sunrise
times.

BUG=953548
TEST=Added new test.

Change-Id: I490fce272bf27a52191762b9dbefbfd89d40238a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1579160
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653301}