[whatwg] EventSource: treating mailto as 204 does not work

[Anne van Kesteren]

For fetching EventSource resources treating mailto as if it was a 204 does  
not work as that reestablishes the connection. The result should be more  
akin a network error of some kind I think. Similarly to how other  
cross-origin requests fail if CORS is not used. I will add some tests for  
this.

--
Anne van Kesteren
http://annevankesteren.nl/