[XHR2] Upload progress events and simple cross-origin requests

[Alexey Proskuryakov]

Per the current XHR2 spec draft, upload progress events are not sent  
if the cross-origin request didn't do preflight. What is the rationale  
behind this requirement?

I used to think that this was necessary to prevent port scans of  
internal networks, but that can be done via other mechanisms anyway,  
as far as I know.

- WBR, Alexey Proskuryakov