code: function computeContentMd5(req) {
      if (req.service.willComputeChecksums(req)) {
        var md5 = AWS.util.crypto.md5(req.httpRequest.body, 'base64');
        req.httpRequest.headers['Content-MD5'] = md5;
      }
    }
docs: A listener that computes the Content-MD5 and sets it in the header.
  @see AWS.S3.willComputeChecksums
  @api private