Added CSS to change scrollbar in chrome

Default scroll-bars in chrome was breaking the overall user interface of pdfjs. So I used the background color and images that are used to create header and created the scroll-bar css for chrome. Please check the attached image.

![scroll1](https://f.cloud.github.com/assets/840971/371575/7a41b552-a33c-11e2-85d6-78a0eae97efe.png)