buffet: Add CommandInstance::ToJson

Method is needed to implement commands status requests from
privetd. Current implementation generates JSON on request.

BUG=brillo:430
TEST=unittest

Change-Id: Iee4a788792a33278c997ad535abe11f26fa7f422
Reviewed-on: https://chromium-review.googlesource.com/262215
Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
6 files changed
tree: 4f603c401756ef267c96acf5dd90c52c7e7e7b35
  1. buffet/