The leak is introduced by #142344
The leak does not repro on mac, but repros on Windows, with bots.
PR that repros the leak: #142414

Can it by test only because of using FakeFlutterView?

Code that creates not disposed objects:

  @override
  RenderObjectElement createElement() => _RawViewElement(this);

  @override
  RenderObject createRenderObject(BuildContext context) {
    return _deprecatedRenderView ?? RenderView(
      view: view,
    );
  }

Failing test: runApp throws if given a View