code: function _removeAndInstall(packagePath, installDirectory, validationResult, callback) {
      // If this extension was previously installed but disabled, we will overwrite the
      // previous installation in that directory.
      fs.remove(installDirectory, function (err) {
          if (err) {
              callback(err);
              return;
          }
          _performInstall(packagePath, installDirectory, validationResult, callback);
      });
  }
docs: Private function to remove the target directory and then install.
  
  @param {string} Absolute path to the package zip file
  @param {string} Absolute path to the destination directory for unzipping
  @param {Object} the return value with the useful information for the client
  @param {Function} callback function that is called at the end of the unzipping