As of January 2019 Google released their own extension for same exact purpose so I recommend switching to it https://chrome.google.com/webstore/detail/picture-in-picture-extens/hkgfoiooedgoejojocmhlaklaeopbecg/
Picture in picture mode can be forced with this extension even if website doesn’t support it.
Ways to use extension
Click the extension icon whenever any kind of video is present on the current page.
* Right click on the video and click “Force picture in picture mode”
* `Alt + shift + s` on Windows or `Cmd+Shift+S`on Mac whenever video is present on the page
* Click PiPPY icon which is embedded in supported players(current only Twitch.tv)
Extension uses icons which are provided by https://icons8.com