metrics_daemon: restore correct meaning of Logging.DailyUse.

Maintain separate persistent values for DailyActiveUse and
CumulativeActiveUse.  The latter is used to compute crash rates
relative to active use.

BUG=chromium:364746
TEST=manual

Change-Id: I4d0485016eb49b30a77169ba1cedc1ffbff8810e
Reviewed-on: https://chromium-review.googlesource.com/195698


Reviewed-by: Daniel Erat <derat@chromium.org>
Reviewed-by: Luigi Semenzato <semenzato@chromium.org>
Tested-by: Luigi Semenzato <semenzato@chromium.org>
Commit-Queue: Luigi Semenzato <semenzato@chromium.org>