BETA version -- 5.0.1002.182

[bufce2010]

In (chrome://settings/cbTabOptions), there is a "When middle clicking on the tab bar" option that can be set to pin/unpin current tab using the drop down menu to the right of that entry. 

Maybe that will suffice for you unless you want the function to work only when there are no other tabs besides the one you want to pin/unpin?

unfortunately I need both options each separately, they existed in version 4.3: Middle mouse on tab to close it, middle mouse on empty tab bar to pin/unpin