According to a few commits in the Chromium Repositories, there is a new button set to join the fray: the microphone mute toggle. While weve had a general audio mute button up in the function row from the outset, theres never been a universal way to quickly toggle the microphone along with the speakers into a muted setting. That looks to be changing.

Source: Upcoming Chromebooks will get a dedicated mic mute keyboard button - Chrome Unboxed

I want this.