Digging in the code also brought up that URL, and it appears as if the entire feature was disabled if Chromium is built without the "Google Chrome branding" fla

Digging in the code also brought up that URL, and it appears as if the entire feature was disabled if Chromium is built without the "Google Chrome branding" flag (and can then be reenabled by specifying a seed URL yourself via command line). Hence one might get by with building from unmodified Chromium source. But the options to disable it on official prebuilt Chrome appear to be grim indeed. SSL interception might not even work at all, as I guess Google uses certificate pinning.