Context: The WPT importer consumes the JSON produced by
git cl try-results is consumed and uses it to determine
when the CQ has passed (whether all non-experimental cq
jobs were successful) and where layout test results are
stored.

Added fields:
  created_ts: This could be used to sort builds by time.
  tags: Includes user_agent tag and experimental tag, as well as
  experimental: whether the job is experimental

Bug: 792652
Change-Id: Ic6099a21b21db668b88b1a8e54aefd84529a2a91
Reviewed-on: https://chromium-review.googlesource.com/819573
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>