FIX: It seems that in Chrome 25 there are a couple of changes that break the scroll emulator:

1) If the ::scrollbar pseudo class selector is present it stops the ::-webkit-scrollbar pseudo class from working.
2) Jonathan Sharp's method for measuring scrollbar width no longer works.

To fix these issues I updated the scrollbarWidth() method with a new approach that works in Chrome 25, and removed the ::scrollbar pseudo class selectors.