As of today the code delivered through https://platform.twitter.com/widgets.js creates shadow DOM on <twitterwidget> element.
On Chrome, this element has a shadow root, but it is created via element.createShadowRoot which is V0 API and obsolete, this should be replaced with V1 API (element.attachShadow).
See the Chrome’s tracking bug for V0 API deprecation:
https://bugs.chromium.org/p/chromium/issues/detail?id=671907
For difference between v0 and v1 API, please refer to:
https://hayato.io/2016/shadowdomv1/