It's a very simple chrome extension hacked together. The one file with functional JS should be pretty self explanatory.
content.js is where the functionality happens, manifest.js organizes everything and the extension includes jQuery even though I the extension is so tiny and I could have easily done without it and made it more lightweight, but I'm lazy.
Enjoy. Copying this application and editing it to your hearts content should help you get started with making Chrome extensions. They are lots of fun.