Chrome Version       : 65.0.3325.51
OS Version: OS X 10.13.3
URLs (if applicable) : https://davidben.scripts.mit.edu/speech-test.html
Other browsers tested:
  Add OK or FAIL after other browsers where you have tested this issue:
     Safari: FAIL
    Firefox: OK
    IE/Edge: (didn't test)

What steps will reproduce the problem?
1. Go to https://davidben.scripts.mit.edu/speech-test.html
2. Look at the tab
3. Right-click the tab and mute it
4. Get very annoyed.

What is the expected result?
There is an indicator that the tab is making sound, like we do for all other sound. Also muting it should work.

What happens instead of that?
Speech synthesis bypasses both of these. It ultimately dumps the data into a system service, so everything we do to control and surface sound must be reimplemented to account for this API, if it is left in its current form.

Please provide any additional information below. Attach a screenshot if
possible.

I came across a frame-busting ad that was abusing this this morning.

(felt, ainslie: palmer suggested I CC you on this since it involves UI bits not working.)

UserAgentString: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.51 Safari/537.36