While it's true that bugs like this exist in Chrome, it requires a malicious site to deliver the exploit. I would like to point out that Enhanced Steam is not exploiting this bug in any way, and that using this feature does not cause Chrome to continue listening to your microphone after the feature has been used.
This is yet another reason why the source code for Enhanced Steam is released as open source and is view-able
here. For those who prefer not to have this feature at all, it will of course be configurable in the options.