Fix java.lang.ClassCastException in requestAnimationFrame

The parameter to a FrameRequestCallback is not an Int, but a `DOMHighResTimeStamp`

http://www.w3.org/TR/hr-time/#domhighrestimestamp

    A DOMHighResTimeStamp SHOULD represent a number of milliseconds accurate to a thousandth of a millisecond.

So (at least in Chrome), a java.lang.ClassCastException is thrown immediately upon entry, since the input is rarely an integer.  This should fix that.