depend on required-components-list from org.mate.session.gschema.xml

<key type="as" name="required-components-list">
<default>[ 'windowmanager', 'panel', 'filemanager' ]</default>
<summary>Required session components</summary>
<description>List of components that are required as part of the
session. (Each element names a key under "/desktop/mate/session/required_components").
The Startup Applications preferences tool will not normally allow users to remove
a required component from the session, and the session manager will automatically add the
required components back to the session at login time if they do get
removed.</description>
</key>