watchOrUnwatchCallback = function (err) {
                if (err) {
                    console.error("FileSystem error in _handleDirectoryChange after watch/unwatch entries: " + err);
                }

                if (--counter === 0) {
                    callback(addedEntries, removedEntries);
                }
            }
Notify the filesystem that the given directory has changed. Updates the filesystem's
internal state as a result of the change, and calls back with the set of added and
removed entries. Mutating FileSystemEntry operations should call this method before
applying the operation's callback, and pass along the resulting change sets in the
internal change event.

@param {Directory} directory The directory that has changed.
@param {function(Array<File|Directory>=, Array<File|Directory>=)} callback
     The callback that will be applied to a set of added and a set of removed
     FileSystemEntry objects.