[geometry] DOMMatrix and WebKitCSSMatrix

[Simon Pieters]

FYI, in https://github.com/whatwg/compat/issues/19 it is suggested to  
change DOMMatrix to be more compatible with WebKitCSSMatrix. I have not  
looked into the details yet, but it seems this should be possible and  
still also be compatible with SVGMatrix, which seems nice.

--
Simon Pieters
Opera Software