anchor.diff:  
     /**
      * The request headers.
  +   *
  +   * The returned [HttpHeaders] are immutable.
      */
     HttpHeaders get headers;
   
  
positive.code:   int contentLength;
  
    /**
     * Returns the request headers.
     */
    HttpHeaders get headers;
  
  
negative.code:    * the official HTTP status codes use the fields from
     * [HttpStatus]. If no status code is explicitly set the default
     * value [HttpStatus.OK] is used.
     *
     * The status code must be set before the body is written
     * to. Setting the status code after writing to the response body or
     * closing the response will throw a `StateError`.
     */
    int statusCode;
  
    /**
     * Gets and sets the reason phrase. If no reason phrase is explicitly
     * set a default reason phrase is provided.
     *
     * The reason phrase must be set before the body is written
     * to. Setting the reason phrase after writing to the response body
     * or closing the response will throw a `StateError`.
     */
    String reasonPhrase;
  
  