code: func NewSPDYExecutorForProtocols(transport http.RoundTripper, upgrader spdy.Upgrader, method string, url *url.URL, protocols ...string) (Executor, error) {
  	return &streamExecutor{
  		upgrader:  upgrader,
  		transport: transport,
  		method:    method,
  		url:       url,
  		protocols: protocols,
  	}, nil
  }
docs: // NewSPDYExecutorForProtocols connects to the provided server and upgrades the connection to
  // multiplexed bidirectional streams using only the provided protocols. Exposed for testing, most
  // callers should use NewSPDYExecutor or NewSPDYExecutorForTransports.