code: function dryRunOrWriteFile(dryRun, filePath, result) {
    var css = result.css;
  
    return new Promise(function (resolve) {
      return resolve(dryRun ? doDryRun(css) : writeCriticalFile(filePath, css));
    });
  }
docs: Do a dry run, or write a file.
  
  @param {bool} dryRun Do a dry run?
  @param {string} filePath Path to write file to.
  @param {Object} result PostCSS root object.
  @return {Promise} Resolves with writeCriticalFile or doDryRun function call.