http://www.w3schools.com/). Once that is understood, I would start reading
about Chrome/Chromium extensions (
http://developer.chrome.com/extensions/getstarted.html). Finally, I would
browse through some examples from
http://developer.chrome.com/extensions/samples.html. That is all you need
to know. Don't worry, it's not so hard, but it may take you a while to get
a grip on the things.
To do that project, you need just to know about content scripts and event
to look nice ;) ).
It is also recommended to have a look at DOM (from W3Schools - don't worry,
create/access/modify/destroy dynamically the elements from a HTML page).
Further reading: AJAX and jQuery.
That's all, I think. Good luck!