With the latest stable release of Chrome, version 46, Google has removed the always-listening feature that let users simply say "Ok Google" to start a voice search in the browser. Citing generally low user adoption, Google removed the feature from Chrome for Windows, Mac and Linux — it's sticking around, at least for now, on Chrome OS.
Voice search isn't going away entirely, though — with this latest update you'll still be able to click the microphone to perform voice searches on google.com and the new tab page. Users on the stable channel of Chrome should see the update hitting their computers now.
Chrome 46 also brings a handful of other changes, with Android users gaining new in-browser media controls that should be easier to use.