Emitted when one or more D-Bus properties on proxy changes. The local cache has already been updated when this signal fires. Note that both changed_properties and invalidated_properties are guaranteed to never be NULL (either may be empty though).
If the proxy has the flag G_DBUS_PROXY_FLAGS_GET_INVALIDATED_PROPERTIES set, then invalidated_properties will always be empty.
This signal corresponds to the PropertiesChanged D-Bus signal on the org.freedesktop.DBus.Properties interface.