Skia Tree Status

Design doc for multi-repo support is here.

How to add support for a repo to tree status

1. Add a --repo=${repo} flag to tree-status.yaml for public repos or

   tree-status-internal.yaml for private repos and push.

2. If the repo has SkCQ, then add to it's infra/skcq.json file:

   For public repo-

   "tree_status_url": "https://tree-status.skia.org/${repo}/current"

   For private repo-

   "tree_status_url": "http://tree-status-internal:8001/${repo}/current"

3. If the repo has a status page, then it's tree status should automatically

   show up on the status page after step 1. This is possible due to the work in

   skbug/12394.

4. The skiastatus plugin on Gerrit will automatically show the repo's tree

   status after step1. This is possible due to the work in

   skbug/12395.