This feature is available in Chrome, but Opera is a much nicer (and faster) browser.
In Chrome, I've found that I use the mute feature a lot. It's great for muting irritating adverts, or if you're listening to music (on Youtube or another online service, such as an online radio)and you want to watch a video then you can just mute it.
This is a great feature and it would be great to see it in my favorite browser.