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.