code: function _handleFileSystemChange(event, entry, added, removed) {
          // this may have been called because files were added
          //  or removed to the file system.  We don't care about those
          if (!entry || entry.isDirectory) {
              return;
          }
  
          // Look for a viewer for the changed file
          var viewer = _viewers[entry.fullPath];
  
          // viewer found, call its refresh method
          if (viewer) {
              viewer.refresh();
          }
      }
docs: Handles file system change events so we can refresh
  image viewers for the files that changed on disk due to external editors
  @param {jQuery.event} event - event object
  @param {?File} file - file object that changed
  @param {Array.<FileSystemEntry>=} added If entry is a Directory, contains zero or more added children
  @param {Array.<FileSystemEntry>=} removed If entry is a Directory, contains zero or more removed children