Hard crash calling Context2d.prototype.filter

[tolmasky]

This line will crash node:

Context2d.prototype.filter

Perhaps worse, so do this:

Object.getOwnPropertyDescriptor(Context2d.prototype, "filter")

I think this is because GetFilter doesn't have a HasInstance guard. I think it should do something along the lines of

if (!HasInstace(this)) return default_value

(as opposed to throwing, since then getOwnPropertyDesctipor would throw. This would match Array.prototype.length for example which is 0).