Chrome has actually changed the way their plugs in work. They now use extensions instead of plug ins. You should still be able to view the Slingbox, you just wouldn't be able to use Chrome for any setup processes. It is now a pop out player. Try these steps below to activate it:
1. Click on the Chrome menu (or press Alt+E)
2. Select Settings
3. Click on the link titled ‘Show advanced settings‘
4. Under the section headed ‘System’ untick the box next to “Continue running background apps when Google Chrome is closed”
Then, close the Settings window and try installing the extension again.
Hope this helps!