void markNeedsToResortDirtyElements()

Flags the dirty elements list as needing resorting.

This should only be called while a buildScope is actively rebuilding the widget tree.

Source 

void markNeedsToResortDirtyElements() {
  assert(() {
    if (debugPrintScheduleBuildForStacks)
      debugPrintStack(label: 'markNeedsToResortDirtyElements() called; _dirtyElementsNeedsResorting was $_dirtyElementsNeedsResorting (now true); dirty list is: $_dirtyElements');
    if (_dirtyElementsNeedsResorting == null) {
      throw new FlutterError(
        'markNeedsToResortDirtyElements() called inappropriately.\n'
        'The markNeedsToResortDirtyElements() method should only be called while the '
        'buildScope() method is actively rebuilding the widget tree.'
      );
    }
    return true;
  });
  _dirtyElementsNeedsResorting = true;
}