I can confirm that with Sage 9 you have to add add_theme_support('soil-google-analytics', 'UA-XXXXX-Y')in your setup.php after all the other add_theme_support calls that are already there.
Also, perhaps it’s obvious but for me it wasn’t:
for this to work you have to install the Soil plugin manually!
This thread covers this embarrassing ignorance from me: Google Analytics via Soil: GA code not appearing anywhere - #15 by trainoasis