Event: fixing incorrect window bug with scrollTop/Left in iframes

The iframe was getting the parent window's value for pageXOffset and pageYOffset, see #1945.

Regardless of what's the resolution of jquery/qunit#356, I agree with [this comment](https://github.com/jquery/qunit/issues/356#issuecomment-10712415) from @jzaefferer: using `expect` makes the intention explicit so I like it better.