[eventsource] Connection close on EventSource collection

> 10 Garbage collection
> If an EventSource object is garbage collected while its connection is
still open, the connection must be closed.

Multiple EventSource instances may share the same underlying connection.  If
this happens, and just one EventSource object is collected (eg. a tab
closed), the connection shouldn't be closed--it's still in use.

Should this instead cancel the fetch algorithm for the EventSource, as with
"aborting a document load" (HTML5)?

-- 
Glenn Maynard