Shameless plug: I wrote Surplus, which is a Chrome extension which does pretty much that. It basically adds that notification icon the the Chrome browser interface, and allows you to post things right from inside the extension. The address bar integration does seem like a cool feature to add, as does auto-hiding, but for now, I think it's close to what you're looking for :)

https://chrome.google.com/webstore/detail/pfphgaimeghgekhncbkfblhdhfaiaipf