Was just going to re-enable NPAPI plugins in Chrome, and I found this:

chromeflags-tabaudiomute

Now that's cool! Slightly weirdly, I love exploring the about:flags page in Chrome (Canary, or otherwise) and finding things in various stages of development - and I always loved the functionality that allowed you to see which tab was playing audio.

On hover:
chromeflags-tabaudiomute-mouseover Context Menu:
chromeflags-tabaudiomute-contextmenu