code: function preferencesReload() {
      return this.initializedPromise.then(function () {
        this._readFromStorage(DEFAULT_PREFERENCES).then(function(prefObj) {
          if (prefObj) {
            this.prefs = prefObj;
          }
        }.bind(this));
      }.bind(this));
    }
docs: Replace the current preference values with the ones from storage.
  @return {Promise} A promise that is resolved when the preference values
  have been updated.