The GCM Play/Pause button will be added to Chrome's desktop versions for Windows, Mac, and Linux. No word on Chrome OS, but it's very likely that the button will work there as well.

While Microsoft tries to get our game systems to be more like TVs, Google is taking our web services and making them more like a game console. Because APPARENTLY WE NEED TO PLAY GAMES ALL THE TIME ...

The play/pause button is located on the toolbar (in Chrome Canary nightly builds for now) as a quick and easy way to control media playback in any tab with a single click or tap.