Add Login.UsersActiveWeekly UMA metric.

BUG=chromium:365352
TEST=manual

Change-Id: Idfa406308ea4b37b89c82d97f1091bcee950017e
Reviewed-on: https://chromium-review.googlesource.com/202280
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Tested-by: Alexander Alekseev <alemate@chromium.org>
Reviewed-by: Bertrand Simonnet <bsimonnet@chromium.org>
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
1 file changed