When disk is low /usr/sbin/chromeos-cleanup-logs send statistics via UMA:

- Platform.DiskUsage.UsersOnDevice : the number of user on device

- Platform.DiskUsage.${dir}_[Max|Avg].${users_category}

where dir is in [Cache Downloads GCache] and users_category in [1User, 2Users,  ... , 7OrMoreUsers].

The later family of variables have been obsoleted  with https://codereview.chromium.org/1934723002.
I could not find them in UMA anyway.

I wonder if their construct (see https://chromiumcodereview.appspot.com/19700006/patch/22001/23001) using fieldtrial is still supported.