anchor.diff:    void flush() {
       if (_map.isNotEmpty) {
         _storageArea.set(_map);
  -      _logger.info('saved preferences: ${_map.keys}');
  +      _logger.warning('flushed: ');// + _map.toString());// _map.keys.fold('', (str, key) => '$str, $key=${_map[key]}'));
         _map.clear();
       }
   
  
positive.code:       return new Future.value(_map[key]);
      } else {
        return _storageArea.get(key).then((Map<String, String> map) {
          // TODO(ussuri): Shouldn't we cache the just read value in _map?
          final String val = map == null ? null : map[key];
          return val != null ? val : defaultVal;
        });
  
negative.code:  * A PreferenceStore backed by `chome.storage.local`.
   */
  PreferenceStore localStore = new _ChromePreferenceStore(
      chrome.storage.local, 'local', new Duration(milliseconds: 100));
  
  /**
   * A PreferenceStore backed by `chome.storage.sync`.
   */
  PreferenceStore syncStore = new _ChromePreferenceStore(
      chrome.storage.sync, 'sync', new Duration(milliseconds: 100));
  
  /**
   * Preferences specific to Spark.
  