(After #14559 merges)
We currently can only check if a document is fully active; however, there are places in the spec that require us to check if the document is just active (example: https://html.spec.whatwg.org/multipage/webappapis.html#dom-document-write step 3 whatwg/html#2216). We need to implement a flag to keep track of this.

cc @asajeffrey