Allow closing the last tab to close the entire window

[bgrins]

STR:
Open a second window
Close the first tab

Expected:
The window disappears

Actual:
A new tab reopens and the window stays around until you close it using the window controls

[jsantell]

We haven't really thought about windows much at all. Should flesh out what we actually want them to do rather than picking and choosing

[bgrins]

I'd say matching Firefox behavior makes sense (even if that means picking and choosing things that begin to match that behavior). Agree it'd be helpful to map out these scenarios across platforms so we can keep track of progress though