In Chrome, you can edit your resources in line and Chrome will generate revisions of that resource. Here the documentation: http://code.google.com/intl/en-US/chrome/devtools/docs/elements-styles.html#persist
Sadly, it’s not working here, and I don’t know how to enable it. It is not possible to expand the file in the resource tab to see the revisions.
Using Chrome 15.0.874.121 on MacOS here. A colleague of mine tried the developer channel, but it’s still not there. But I saw a demo of it at the Google Developer Day.
This works in 15.0.874.121 as well — just double-click on a text content of a CSS or JS file in the Resources panel, type something and press Cmd+Enter. You will see the lines that you added displayed with a green background, and the edited resource on the left will become expandable.