Also adds tests for the bug and for --json output.

R=agable@chromium.org, phajdan@chromium.org

Change-Id: I4e2208fdad8e23d48d27d0a354470336a7b86180
Reviewed-on: https://chromium-review.googlesource.com/570030Reviewed-by: Paweł Hajdan Jr. <phajdan.jr@chromium.org>
Commit-Queue: Paweł Hajdan Jr. <phajdan.jr@chromium.org>