Of course they can, it's about the marketshare and not the code. They can make some part of the browser running in their cloud services and no matter how much y

Of course they can, it's about the marketshare and not the code. They can make some part of the browser running in their cloud services and no matter how much you look into the Chromium code the websites which support this will run in Chrome only. Why would websites support this? Well, it can provide good rankings in search or some other goodie like speeding up the loading times through Google CDN or something and works for %90 of the people(because they use Chrome). Once enough websites integrate this, it's over.