code: function(syncOptions, serverResponses) {
      const syncs = [];
      if (syncOptions.iframeEnabled) {
        for (var index = 0; index < serverResponses.length; index++) {
          if (serverResponses[index].body && serverResponses[index].body.trackingPixel) {
            syncs.push({
              type: 'iframe',
              url: serverResponses[index].body.trackingPixel
            });
          }
        }
      }
      return syncs;
    }
docs: Register the user sync pixels which should be dropped after the auction.
  
  @param {SyncOptions} syncOptions Which user syncs are allowed?
  @param {ServerResponse[]} serverResponses List of server's responses.
  @return {UserSync[]} The user syncs which should be dropped.