Use case

Developers wanting to retrieve the brightness for a MaterialApp currently have to look it up directly from the Theme, i.e Theme.of(context).brightness .

Proposal

Add Theme.brightnessOf(context) and Theme.maybeBrightnessOf(context), which would be the Material equivalent of

https://api.flutter.dev/flutter/cupertino/CupertinoTheme/brightnessOf.html
https://api.flutter.dev/flutter/cupertino/CupertinoTheme/maybeBrightnessOf.html

This also opens the door to having the Brightness as an aspect, if Theme ever becomes an InheritedModel.