The Chrome extension named "Web Developer" by Chris Pederick has been compromised and is injecting ads into web pages. Version 0.4.8 is the latest version released by the developer, and the compromised version is 0.4.9. If you're using this extension, you should disable or remove it immediately.

The extension page in the Chrome Web Store appears to have been removed, so I'm guessing Google (automated or otherwise) is aware of this.