code: func NewURLBuilder(addr *types.StreamAddr) *ViewerURLBuilder {
  	prefix, _ := addr.Path.Split()
  	return &ViewerURLBuilder{
  		Host:    addr.Host,
  		Prefix:  prefix,
  		Project: addr.Project,
  	}
  }
docs: // NewURLBuilder creates a new URLBuilder that can generate links to LogDog
  // pages given a LogDog StreamAddr.