Add headless Chrome support with libgtk-3-0

[vangberg]

We are using https://github.com/addyosmani/critical to generate critical CSS as part of the build process. Critical uses headless Chrome behind the scenes, which currently fails on Netlify:

5:26:24 PM: (node:866) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Error: Failed to launch chrome!
/opt/build/repo/node_modules/puppeteer/.local-chromium/linux-499413/chrome-linux/chrome: error while loading shared libraries: libgtk-3.so.0: cannot open shared object file: No such file or directory


TROUBLESHOOTING: https://github.com/GoogleChrome/puppeteer/blob/master/docs/troubleshooting.md
5:26:24 PM: (node:866) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

The only missing part is libgtk-3-0. With that installed, it works.

[aaronshaf]

Same problem here

[calavera]

LGTM