The removal of this preference was botched, all other surrounding plumbing changes appear to be working okay. The ability to use prefs to control this stylesheet might be useful in the future, so perhaps this is one of those "if it ain't broke, don't fix it" bugs where leaving well enough alone in the first place would have been the best choice.
* Implementation for assignedNodes
* Include slots in the flat tree
* Fix event get-the-parent algorithm for a node
* Update and add reftests for Shadow DOM v1
* Update web platform tests expectations
Tag #1375
