The logic for tracking this should move over to SystemNetworkContextManager, and the setting set on the NetworkService object itself (See  issue 846883  for discussion on a similar setting).  This should wait until after https://chromium-review.googlesource.com/c/chromium/src/+/1067959 lands.

This should only block canary if we start experimenting with DoH before then.  If not, then this should block experimenting with DoH.