This is hyperbolic.
First, Chrome is closed-sourced so it can in theory be doing all kinds of things even worse than listening in.
Second, Chromium, the open-source browser that Chrome is based on, shows that the binary blob that does this listening in is in its own sandbox with a well-defined interface to the rest of the world. That interface can enable connection to the microphone if the hot word option is enabled in the browser, which is by default disabled. All of those facts can be verified by studying the interface because Chromium is open source.
The reality is that the modern browser is a software platform just like the OS. And I would argue that running any closed-source software on your OS is analogous to running these binary blobs in the browser, except in practice it is even worse because a modern browser has better sandboxing enforced than today's desktop OSes (mobile OSes, like iOS and Android, are much better on this front). So unless you are an open source purist
 and every single piece of software in the stack running on your system from the user-facing applications to the kernel is open source (and I doubt the firmware to make your hardware devices work is open source), then I find objections to binary blobs running in the browser platform in secure sandboxes with well-defined open-source interfaces to be a bit hypocritical.
Edit: Anyway, apparently they now disabled it for the default build of Chromium (https://code.google.com/p/chromium/issues/detail?id=500922#c31
). And I assume this will be the build configuration that will be used for official binaries provided from the repositories of popular Linux distros. Obviously Chrome (which is not open source) will be unaffected by this change.
 And before anyone complains, I know the difference between open source and free software. I realize Stallman would be a free software
purist. But by definition free (libre) software is a superset of open source software, thus a free software purist would also necessarily be an open source purist.