code: function CompleteMultipartUpload(fileUpload) {
              fileUpload.info('will attempt to complete upload');
              var request = {
                  method: 'POST',
                  contentType: 'application/xml; charset=UTF-8',
                  path: '?uploadId=' + fileUpload.uploadId,
                  x_amz_headers: fileUpload.xAmzHeadersCommon || fileUpload.xAmzHeadersAtComplete,
                  step: 'complete'
              };
              CancelableS3AWSRequest.call(this, fileUpload, request);
          }
docs: http://docs.amazonwebservices.com/AmazonS3/latest/API/mpUploadComplete.html