The extension is available in the Chrome Web Store here.
Most users and organizations should be able to use the version in the Chrome Web Store without needing to compile it themselves. Google for Work enterprises can configure settings using managed storage as described in the deployment guide.
./do.sh install_deps
./do.sh build_extensionYou'll only need to install_deps the first time you build the extension. To see other options, run do.sh with no arguments.
This seems really unlikely.
Calculating a hash in JavaScript on every keystroke sounds expensive, but it's actually fast enough to not have a noticable impact.