If a page has a form interaction, processes the form and removes the form from the DOM, we don't unset that bit. That means that we won't discard the tab because we believe their's some user content on the page.

This probably makes sense for now when we want to be most conservative, but we might want to make that bit represent the current state of the page in the future as we try to apply tab discarding to more content.

As it is, if you interact with the search box in gmail, facebook, etc, then we will make the page has having had form interaction and exclude it from being discardable.

Maybe in the medium-term we should at least UMA how much of a difference it makes in % discardable tabs.