Hello,
I'm interested by your project since I have already done a Chrome extension that was doing something a bit close to what you're asking. The extension I developed was analyzing the current tab and if the user was on the current tab at a specific address, then analyze the page, find some information, make a research and edit the page (it was in fact retrieving the file name of an episode of a tv serie uploaded on a site and determined the serie, title of episode and description from IMDb). So I think I can help you with your project.
Best regards,
Laurent.