The UI service has (at least) two unique sets of clients ( https://chromium.googlesource.com/chromium/src/+/master/services/ui/manifest.json ) . There is the typical client, 'app', and the 'window_manager'. Both of these classes have a core set that is the same, and then a couple of unique interfaces. Currently this is done by duplicating the interfaces between the two classes. It would be nice if there was a way to define a group that the other two groups referred to, e.g.:

common: [ the common interfaces ]
app: [common, app-specific interfaces]
window_manager: [common, wm-specific interfaces]