[mediacapture-image] Use DOMPoint instead of Point2D?

dontcallmedom has just created a new issue for 
https://github.com/w3c/mediacapture-image:

== Use DOMPoint instead of Point2D? ==
from @w3ctag 's 
[review](https://github.com/w3ctag/spec-reviews/issues/133#issuecomment-270259285)
 @travisleithead:
> Consider allowing a DOMPoint in places where a Point2D dictionary 
could be used (DOMPoint from 
http://www.w3.org/TR/geometry-1/#DOMPoint). The DOMPoint handles 
points in 3d space, but the 'z' and 'w' coordinates are not required, 
and this may be useful for platform consistency. 

Please view or discuss this issue at 
https://github.com/w3c/mediacapture-image/issues/145 using your GitHub
 account