In  bug 752083  debug builders were added to the chromium.webrtc.fyi waterfall in order to get protection against debug-only compile breakages. These bots are only used for compile so there's no need to archive their build output (it's very wasteful since the size is very large), since no tester is downloading it, see https://cs.chromium.org/chromium/build/scripts/slave/recipe_modules/chromium_tests/chromium_webrtc_fyi.py
The chromium_tests recipe module wasn't structured in a good way to make that possible however, so there's a "package build" step taking place on these builds. 

Example build where the package build step takes 14 minutes and archives 4.93GB to Google storage for no use:
https://build.chromium.org/p/chromium.webrtc.fyi/builders/Win%20Builder%20%28dbg%29/builds/492