This description is not very clear. Can you clarify what the issue is?

FWIW, it's useful for debugging purposes to have a minimal amount of necessary code changes to exercise the full UMA upload path in developer builds.

The problem is not with developer build but when you build chromium build. In that case UMA bit starts as OFF but then the user can go and turn UMA bit ON.

This leads to inconsistent behavior as in some places only the pref value is read and in other places it is also checked that it is Chrome build.
For example in this case UMA logs will be uploaded but about:crashes will show that crashes are disabled.