(2) is indeed WAI (all preferences are per-profile).  I can see an argument for (1), though.  I would go further and say that all profiles that had any open window at last exit should be reopened, using each profile's relaunch settings.  In your case, that would mean restoring all three profiles, loading just a new tab in the third profile.

[mac triage]

both

void ChromeBrowserMainPartsWin::RegisterApplicationRestart(..)

and

void ChromeBrowserMainPartsMac::PreEarlyInitialization()

have codepaths that add `switches::kRestoreLastSession`

Session restore doesn't seem to do much with kRestoreLastSession though.

The presence of  Issue 630618  suggests it's possible to restore multiple profiles at once (but also that there are dragons when trying to do that). This will need further investigation.

Migrating to more generic platform label, so that it can be applied to other platforms (i.e. I love the idea).

I have this, too, Linux GNOME Shell.

If Chromium is exited using GNOME top bar - Chromium Web Browser - Quit,
then only the last closing profile is opened on relaunch

If Chromium is opened by selecting ⋮ - Exit,
then all profile reopen on relaunch

Version 55.0.2883.87 Built on Ubuntu , running on Ubuntu 16.10 (64-bit)

+ewald, this would be good to improve for multi-profile users. Possibly related to issue 130656?

Hmmmm, right now on Mac Canary, I'm observing the "desired" behavior from comment #0. Specifically, if I quit Chrome (by going Chrome > Quit Google Chrome) with two profiles open and then re-open Chrome, both profiles are opened, and their respective startup prefs are honored.

Any ideas why I'd be seeing that on Canary?

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