src/bugsnag: do not polyfill requestAnimationFrame

[kyrylo]

Fixes #72 (requestAnimationFrame wrapper doesn't honor the passed
timestamp)

What's the point, really? It doesn't have anything to do with
hijackTimeFunc at all.

[jmshal]

The point of having a function like requestAnimationFrame wrapped, is due to the fact the callback is invoked asynchronously. Meaning, doing something like the following, would not work.

try {
    window.requestAnimationFrame(function () {
        throw Error('Foobar');
    });
} catch (e) {
    // The following line never happens...
    console.log('Oh noes!', e);
}

So for older browsers, you loose a lot of information; because the error gets diverted to window.onerror. On new(er) browsers, this isn't a huge deal, because the actual Error object is passed. Wrapping the callback allows us to try catch the original function, when it's actually invoked.