Added WebIDL for the callback itself
SImple invocation for requestAnimationFrame
cancelAnimationFrame does nothing
Assert that SyntaxError DOMException is thrown

Previous commit was merged before Simon's review comments could be addressed (https://critic.hoppipolla.co.uk/r/1506)
Merge pull request #990 from caitp/patch-4

Assert that SyntaxError DOMException is thrown
Merge pull request #931 from plehegar/animation-timing-basic

Animation timing basic