I have recently done work on Chrome, blocking extensions. whitelisting and force installing.
Below is my plist. May be a bit sloppy to some people but it works! (uploaded as a photo as it looks better than copy paste)
Once you have typed it up, save it as com.google.Chrome.plist
Then you have to test it. copy the file and paste it into /Library/Managed Preferences
Open Chome and type chrome://policy and you should see the policies applied come up.
Hope this helps. any questions let me know.
The string for ExtensionInstallBlacklist. * means it will black list everything in the chrome store.
When white listing, you need the Chome extension ID which is found on the URL of the extension in the Chrome Store. I like to add comments after so I remember what is white listed.
If you want to force install a extension. you have to put <string>aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa;https://clients2.google.com/service/update2/crx</string>
then in the next string the Chome extension ID which is found on the URL of the extension in the Chrome Store.