context: https://cs.chromium.org/search/?q=BUILDBOT_MAGIC_ENV&sq=package:chromium&type=cs

There should be a much more explicit user-driven process for including these environment variables in the execution of the recipe. Alternately, when we're off buildbot, assume that the environment IS clean, and we should remove this whitelisting code entirely.

Or we should REALLY clean the whole environment, and have the addition of these envvars be explicit?

Something like that... anyway, having infra and buildbot-specific envvars in the core recipe engine is no bueno.