[whatwg] Using time-origin-relative times for the .timeStamp property of animation events is not web-compatible

[Boris Zbarsky]

It looks like at least the angular-animate assumes that the .timeStamp 
property of animation events produces values that can be compared to 
Date.now() return values.  See 
https://bugzilla.mozilla.org/show_bug.cgi?id=1231619#c3 for details.

-Boris