1) Click on the Google Chrome options on the top right hand corner.
2) Click More Tools and then Extensions
3) If you see the Block Sender app icon make sure that the Enabled check box is ticked.
4) After checking, you can go ahead and login to mail.google.com using Google chrome and login to your account to double check if the buttons are there or not. You can check by opening a message, the Block button should appear to the right of the Delete button.