metrics: Fix metrics_daemon Meminfo callback interval

With the switch from the glib run loop to base::MessageLoop, the
interval for scheduling Meminfo callbacks was incorrectly set to
milliseconds.  Fix it back to seconds.

BUG=chromium:445573
TEST=strace shows metrics_daemon sleep for 30 seconds between
     collecting statistics

Change-Id: I4b4b597273d3cf04b9972011dd0a7386ea14233d
Reviewed-on: https://chromium-review.googlesource.com/238466


Reviewed-by: Chih-Chung Chang <chihchung@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Steve Fung <stevefung@chromium.org>
Tested-by: Steve Fung <stevefung@chromium.org>