[RequestAnimationFrame] cancelRequestAnimationFrame is an odd name

The name is a bit odd, if only because it's not really symmetric with 
requestAnimationFrame.  It took me a bit of staring at it to understand 
what it might actually mean.

Would it make more sense to call this cancelAnimationFrame?  Or if we 
want to emphasize that only one request is being canceled, perhaps 
cancelAnimationFrameRequest?

-Boris