Google Chrome offers an option to visually highlight repainted areas using a Developer Tools option called 'Show paint rectangles'. It is described here: https://developer.chrome.com/devtools/docs/rendering-settings
Another of those options is FPS meter rendering. This option you can even enabled permanently by modifying chrome:flags, but I can't figure out how to permanently enable paint rectangles to be rendered for every page without the Developer Tools console open. There doesn't seem to be a flag for it I could enable.
Is there a solution to this? Maybe a setting or an extension to do it?