antiscroll does not work with chrome Version 25.0.1323.1 dev

Antiscroll stopped working properly in Chrome v25 (it's still in dev channel). For some reason native scrollbars are displayed under the antiscroll generated scrollbars. The browser behaves as if ::scrollbar pseudo class styles (setting scrollbar width/height to 0) were ignored.

![antiscroll in chrome v25](https://raw.github.com/gist/4109074/5220ec90449e2bc5342e389b02a1e7e1ca4a6c6c/antiscroll-chrome-v25.png)

I am not really sure what's causing that, but when trying to investigate the problem I realized that scrollbarSize did not work properly in Chrome. It was returning 0 and not the native scrollbar width.

We now calculate the size in the container with 'antiscroll-inner' classapplied. If ::scrollbar CSS is applied properly the width is 0, and we don't have to hide native scrollbars manually. Otherwise scrollbars are hidden by adjusting .antiscroll-inner size.

That fixes Chrome v25 issue.