These decidedly Google Now like notifications are soon going to be appearing in Chrome very soon according to a recent Google+ post from open-source Chromium Evangelist François Beaufort. He advised that the code has been promoted to the stable build of the Chromium Project, Chrome 28 for those playing at home. The rich notifications are available for ChromeOS and Chrome for Windows only at this stage.
It’s an interesting feature which shows more unification across Google products. This improvement to the notification centre is a very welcome additon, if you’re a developer you can check out the nuts and bolts of the API at the Chrome Developers page.