chromite/venv/chromite is a softlink back to chromite.  This means you can have a path like:
src/third_party/chromite/venv/chromite/venv/chromite/venv/chromite/venv/chromite/venv/chromite

thomasanderson@thomasanderson:~/dev/chromium_official/src$ tools/checklicenses/checklicenses.py 
Using base directory: /usr/local/google/home/thomasanderson/dev/chromium_official/src
Checking: /usr/local/google/home/thomasanderson/dev/chromium_official/src

----------- licensecheck stderr -----------
find: File system loop detected; ‘/usr/local/google/home/thomasanderson/dev/chromium_official/src/third_party/chromite/venv/chromite’ is part of the same file system loop as ‘/usr/local/google/home/thomasanderson/dev/chromium_official/src/third_party/chromite’.

--------- end licensecheck stderr ---------

FAILED