Comment 11 for bug 1847532

@Seth, while we might be able to fix it by moving things in the inheritance structure, that doesn't make it visible, and we'll still end up right back here again at some future date.

Having a "shutdown" call for the tool manager makes sense, especially in light of the fact that it's spinning up virtual event loops. We already have a "shutdown" call for the GAL canvas, so it's not foreign to our control flow.