[cssom-view] addMediumListener / removeMediumListener

Taking no answer to my endorsement of the proposal of David Baron as a  
tentative yes I added addMediumListener and removeMediumListener to the  
draft of CSSOM View. It was a little bit more complex than I thought so  
I'd appreciate it if people gave it a good look for errors. They're part  
of the StyleMedia interface.

http://dev.w3.org/csswg/cssom-view/#the-stylemedia-interface

I re-used terminology as much as possible. The only exception is that I  
used the interface prefix MediaQuery rather than Media (as would be  
logical given MediaList) to prevent potential future clashes with the  
media elements in HTML.


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