Accept the attribute in the generator and, minimally, output something like:
> [Advice ("You must call the base method when overriding.")]
in the generated code.
This will allow the IDE to show the requirement to the developer.
This can be done manually until then,
Ideally we need to update xtro to report missing cases.
@Sebastien, setting this to confirmed to keep the backlog clean and not get confused.
merge in master with https://github.com/xamarin/xamarin-macios/commit/ec744533b9e51f1cb1a748b8a2375195abd0a66a