Features like the updater / appmanager, which is borderline malware and one of the reasons I uninstalled Chrome (and boy did it take some effort). Regardless, Chrome is not fully opensource, so there is no way to "calculate" the % you mention. Google might be running a bitcoin miner in Chrome and you would have no way of knowing.

The degree of trust required to run Chrome is equivalent to the one you need to run Vivaldi; the only difference is who you trust (Google vs a bunch of ex-Opera developers). If you don't trust anything that is not opensource, you shouldn't run Google Chrome - you should run Chromium or Firefox builds published by trusted parties.