Now you can bypass the microphone icon and use the hotword "OK Google" when you're using Google search or the new tab page. You need to install this extension first.
"Chrome will listen for you to say 'Ok Google' and then send the sound of the next thing you say, plus a few seconds before, to Google," informs the options page. By default, Google stops listening after 5 minutes to reduce battery consumption on a laptop.
Hotword detection works offline and doesn't send the recording to Google's servers until you say "OK Google". You need to open a Google search page or go to the new tab page first, assuming that you have the updated new tab page which uses the Google homepage. The extension only works for google.com, not for other Google domains:
You can tell if Google is listening by checking the microphone icon from the search box:
Now Google handles Voice Search queries differently. In addition to providing voice feedback and using the previous query for disambiguation, Google now changes your query and removes unnecessary word. For example, if you tell Google "show me some Brad Pitt movies", Google will show results for [Brad Pitt movies].