https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/frame/deprecation.cc has lots of features which should have been removed, but haven't been yet. This will confuse web developers and possibly have them take our deprecation messages seriously if we keep doing it.

I think we need one of:

Someone to furiously poke people after each branch point until it's taken care of.

Or automatically disabling features based on the milestone we've set.