* [Call.request] is a redirect to a different address.
   *
   * Prior to OkHttp 4.3 this was incorrectly invoked when the client was ready to read headers.
   * This was misleading for tracing because it was too early.
   */
  open fun responseHeadersStart(call: Call) {
  }

  /**
   * Invoked immediately after receiving response headers.
   *