I believe that extension would be https://chrome.google.com/webstore/detail/google-tone/nnckehldicaciogcbchegobnafnjkcne https://chrome.google.com/webstore/deta

I believe that extension would be https://chrome.google.com/webstore/detail/google-tone/nnckehldicaciogcbchegobnafnjkcne https://chrome.google.com/webstore/detail/google-tone/nnckeh... (last updated 3 years ago). Not sure if that was ever something official or just an experiment. There's also (the non-Google) chirp.io that started around the same time.