code: func NewPoolDescriptor(host string, dimensions []string) PoolDescriptor {
  	desc := make([]string, 0, len(dimensions)+1)
  	desc = append(desc, fmt.Sprintf("%s:%s", SwarmingHostnameKey, host))
  	desc = append(desc, dimensions...)
  	sort.Strings(desc)
  	return desc
  }
docs: // NewPoolDescriptor creates a new PoolDescriptor given a swarming hostname
  // and a slice of dimensions.  The dimensions are expected to be in "key:value" format,
  // where the key is the tag name.  This is the same format returned by the Swarming API.