From @jacob314 : "In the Flutter doc comments there are a lot of comments that start with "In checked mode" which should probably be updated to be consistent with Dart 2.
Dart 2 doesn't have a concept of checked vs unchecked mode. In Dart 1, unchecked mode meant ignore all type checks as well as ignore asserts.
In Dart2, --enable-asserts turns on asserts which is technically correct for these comments but a bit of a mouthful."

We should update any doc comments that reference "checked mode" with something appropriate.