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+Son Mac whenever video is present on the page
• Click PiPPY icon which is embedded in supported players(currently only on Twitch.tv)

Extension uses icons which are provided by Icons8