Fix bug that was causing us to lose total memory buckets.

When safely resetting stats after committing them, we were
mistakenly clearing the current memory state so we would lose
that total memory time until the memory state changes again.

Also improve the summary output to print percentages, which
make more sense for that display.

Change-Id: I0fe45fd78e97ec8b94976170dd42f4ed345a5899