"split" mode extension receives no navigation events from multilogin tabs

[derjanb]

"split" mode extensions like Tampermonkey don't get events and messages from multilogin tabs. If a regular incognito mode tab is opened, then a second background page is started that handles incognito tab events, but this doesn't happen for multilogin tabs.

"Allow in incognito" is turned on but `chrome.runtime.onMessage` of neither the regular background page nor the incognito background page receives the messages sent by the multilogin tab's content script.

Note: "Spanning" mode extensions seem to work fine.

Original bug report: https://github.com/Tampermonkey/tampermo...ssues/1295

Thanks.