anchor.diff:    HttpHeaders _headers;
   
     /// The headers associated with the HTTP request.
  -  HttpHeaders get headers {
  -    if (_headers == null) {
  -      _headers = new _SyncHttpClientRequestHeaders(this);
  -    }
  -    return _headers;
  -  }
  +  HttpHeaders get headers =>
  +      _headers ??= new _SyncHttpClientRequestHeaders(this);
   
     /// The type of HTTP request being made.
     final String method;
  
positive.code: }
  
  class _SyncHttpClientRequestHeaders implements HttpHeaders {
    Map<String, List> _headers = <String, List<String>>{};
  
    final SyncHttpClientRequest _request;
    ContentType contentType;
  
negative.code:       }
      }
  
      return new SyncHttpClientResponse._(headers,
          reasonPhrase: reasonPhrase,
          statusCode: statusCode,
          body: body.toString());
    }
  
    SyncHttpClientResponse._(Map<String, List<String>> headers,
        {this.reasonPhrase, this.statusCode, this.body})
        : this.headers = new _SyncHttpClientResponseHeaders(headers);
  }
  
  