The #set-the-ongoing-navigation is used to track navigation aborting and to prevent any navigations from taking place during traversal.

This is called from #navigate, #navigate-to-a-javascript:-url, #apply-the-history-step, #deactivate-a-document-for-a-cross-document-navigation, and #nav-stop.

It calls #inform-the-navigation-api-about-aborting-navigation, which in turn calls #abort-the-ongoing-navigation. It is crucial for us to handle this to keep the invariants of #inner-navigate-event-firing-algorithm

Moving this work to be performed in 1959389.