Array.prototype.contains

[Domenic Denicola]

Thanks very much Boris. It sounds like there isn't much of a cross-browser or standardized story on where `DOMStringList`, with its `contains()` and `item()` methods (yeah, I meant `item`) shows up.

I'd be curious where it shows up in Blink, IE, and WebKit codebases. If the intersection is small enough, such that no web developers are relying on `contains()` and `item()` being present on certain APIs, then maybe `DOMStringList` can be killed and replaced with arrays and/or frozen arrays, without adding `contains()`/`item()` to `Array.prototype`...