code: func getBuildbucketURI(b *buildbot.Build) (string, bool) {
  	v, ok := b.PropertyValue("buildbucket").(string)
  	if !ok {
  		return "", false
  	}
  	var message struct {
  		Build struct {
  			ID string `json:"id"`
  		} `json:"build"`
  	}
  	if err := json.Unmarshal([]byte(v), &message); err == nil && message.Build.ID != "" {
  		return fmt.Sprintf("buildbucket://cr-buildbucket.appspot.com/build/%s", message.Build.ID), true
  	}
  	return "", false
  }
docs: // getBuildbucketURI attempts to extract the buildbucket information from the properties
  // of a buildbot build.  The format is in buildbucket://<host>/build/<buildID>.
  // Because all of our buildbot instances point to cr-buildbucket.appspot.com,
  // <host> is always cr-buildbucket.appspot.com.