code: function performNpmInstallIfRequired(npmOptions, validationResult, callback) {
  
      function finish() {
          callback(null, validationResult);
      }
  
      var installDirectory = path.join(validationResult.extractDir, validationResult.commonPrefix);
      var packageJson;
  
      try {
          packageJson = fs.readJsonSync(path.join(installDirectory, "package.json"));
      } catch (e) {
          packageJson = null;
      }
  
      if (!packageJson || !packageJson.dependencies || !Object.keys(packageJson.dependencies).length) {
          return finish();
      }
  
      _performNpmInstall(installDirectory, npmOptions, function (err) {
          if (err) {
              validationResult.errors.push([Errors.NPM_INSTALL_FAILED, err.toString()]);
          }
          finish();
      });
  }
docs: Checks package.json of the extracted extension for npm dependencies
  and runs npm install when required.
  @param {Object} validationResult return value of the validation procedure
  @param {Function} callback function to be called after the end of validation procedure