How to reproduce:
- Display any file in Diffusion as an anonymous user, e.g. https://secure.phabricator.com/diffusion/ARC/browse/master/src/lint/linter/ArcanistXHPASTLinter.php
- Notice that only phsid cookie exists.
- Click Enable Blame.
- Observe the following error:
Your browser did not submit a "phcid" cookie with client state information in the request. Check that cookies are enabled. If this problem persists, you may need to clear your cookies.