Do you think no-one would notice that the Chrome download was 20GB larger?

Who says they'll be using the 20GB model? You'd hardly need frontier level intelligence to detect CSAM or ad keywords. Moreover, it's downloaded on first use, not bundled with the browser, so you won't really notice unless you're checking the chrome user data directory, but that also contains caches and other site data you'd likely chalk it up to random sites.