Chrome: Sharing links via the internet is easy. Sharing in person is still surprisingly difficult. Google Tone aims to make it easier to pass a link around a meeting table by emitting an audible code that your browser can hear and interpret. That means anyone within earshot can grab the link.
This actually isn't the first time we've seen something like this. Chirp for Android and iOS works along a similar principle. In both cases, the services allow you to share a link with sound, which is handy when you're presenting to an audience or sharing a link in a meeting.
Google Tone is designed with the browser in mind, so it's much more likely to be useful in a setting where your audience has their laptops out, rather than just their phones.