There is also Chromium which you can build and patch if you really need low level changes to the browser not achievable from JS, but nothing immediately comes to mind to necessitate that.
It doesn't look easy to change and even then, there is some doubt whether it works with newer Chrome versions. Anyways, the Chrome developers are purposely making hard if not impossible to change the Referrer and other headers. Part of the blame is to comply with standards but there should be some flag to turn off that behaviour.
There is also Chromium which you can build and patch if you really need low level changes to the browser not achievable from JS, but nothing immediately comes to mind to necessitate that.