Incognito mode is a window-level mode - all pages viewed within this window are not persisted to the user's history, and incognito pages use a temporary cookie store that is blank at the start of the incognito session.

Chromium's backend is capable of running incognito on a per-tab basis, yet we keep the mode at the window level to avoid the confusion of having a tabstrip of mixed-mode tabs.

To avoid having to back-delete a page's history, we do not allow dragging between incognito and regular-mode windows.