Note that the naming of the keys is different from editing gsettings. The keys are named like they show in System Settings > “Keyboard” > “Shortcuts” > “Custom Shortcuts”, as far as I can see.
I tested the script on 12.04 under VirtualBox; it needed a log out/in for the changes to take place.
How to Adjust Default Font or Line Spacing in Google Docs. Create a new document or go into a current document with the formatting you want.