Add cryptohome out-of-process mount metrics.

Metrics were added in https://chromium-review.googlesource.com/c/chromiumos/platform2/+/1958504.
Enums were added in https://chromium-review.googlesource.com/c/chromium/src/+/1976310.

BUG=985492
TEST=validate_format.py, pretty_print.py.

Change-Id: I9ed97d931fbe7877b7d1deb33a5426e9ef8c4011
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1976436
Commit-Queue: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Christopher Thompson <cthomp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726565}