Navigator - Web APIs
properties doesn't inherit any properties, but implements those defined in navigatorid, navigatorlanguage, navigatoronline, navigatorcontentutils, navigatorstorage, navigatorstorageutils, navigatorconcurrenthardware, navigatorplugins, and navigatorusermedia.
... methods doesn't inherit any method, but implements those defined in navigatorid, navigatorcontentutils, navigatorusermedia, and navigatorstorageutils.

Navigator.mediaDevices - Web APIs
specifications specification status comment media capture and streamsthe definition of 'navigatorusermedia.mediadevices' in that specification.