Steps to reproduce the problem:
(i'm doing this on a Pixel tablet)

1. Remote into the console, and do the following:

var s = new SpeechSynthesisUtterance()
s.text = "hey how are you"
s.lang = "en"
s.onend = function(ev){console.log("reached end")}
s.onboundary = function(event){console.log('reached boundary')}
speechSynthesis.speak(s)

The speech synthesis works (you hear the sound), but only the 'onend' event is fired:

undefined
VM2640:2 reached end

What is the expected behavior?
It should log out "reached end" 4 times

What went wrong?
It didn't fire the event at all

Did this work before? No 

Chrome version: 48.0.2564.95  Channel: stable
OS Version: 6.0
Flash Version: 

I have this working fine on desktop Chrome Version 48.0.2564.116 (64-bit)