The option --json-output will make the auto-roller dump a
json file with a monitoring_state key. This can be one of:
started, up_to_date, success.

BUG=chromium:559141
LOG=n
NOTRY=true

Review URL: https://codereview.chromium.org/1465413002

Cr-Commit-Position: refs/heads/master@{#32201}