Fixed the code to make it compatible with the new polyfill however the c...

...onstructor of Animation when a function is passed in is not compatible with the one in the specs Please enter the commit message for your changes. Lines starting
It's better to phrase this as a task:
// FIXME: Update web-animations.js to match EffectCallback spec: function(timeFraction, animation, previousTimeFraction) -> function(timeFraction, target, animation)