Save and restore the state if the app process is killed in the background
The tabs and the state of the WebViews could be stored in the bundle and reapplied when the app is restarted.
It might or might not be possible to save the WebView histories, because I'm not sure there is a way to recreate them based on data that can fit in a bundle.
Note that this is simply the movement of information that is in one part of RAM to a different part of RAM so that it persists if Android's memory management system reclaims the majority of Privacy Browser's RAM usage while it is not in the foreground. It will not create any permanent storage on the flash and will not persist data if Privacy Browser is closed or if the device is restarted. Specifically, if the app ever reaches the `onDestroy()` stage the data will be lost.