Service Worker: Innermost nested iframe for partitioned service workers

Innermost 1p iframe (A2) with 3p ancestor (A1-B-A2-A3): this iframe will register a service worker when it loads and then add its own iframe (A3) that will attempt to navigate to a url. ServiceWorker will intercept this navigation and resolve the ServiceWorker's internal Promise. When ThirdPartyStoragePartitioning is enabled, this iframe should be partitioned from the main frame and should not share a ServiceWorker.