The debugger UI currently does not handle tabDetached events at all, relying on unload events instead. This is not a practical problem at the moment, but debugging a remote instance with no access to its unload events wouldn't work.
Created attachment 568100 [details] [diff] [review]
The tabDetached handler may have to do different work when we support debugging remote instances, but this should suffice for now.
Another change is that BrowserTabActor.onDetach now returns "detached" instead of "tabDetached", since we need to differentiate between the unsolicited event and the response to a client-initiated request, but also for consistency with the thread actor response.