Chromite Butler does not appear to understand per-file OWNERS directives that refer to another OWNERS file, e.g.

per-file foo.gypi=file://components/foo/OWNERS

It appears to interpret the owner of foo.gypi to be "file://components/foo/OWNERS", rather than looking at the contents of that file. For a concrete example, see https://codereview.chromium.org/2066553002/. The file "components/certificate_transparency.gypi" appears with a red box next to it labeled "No OWNER for this file in the reviewer list", yet one of the reviewers (Eran Messeri) is an owner of that file.