Where might this entry reside in the User Preferences > Input list? I would like to assign it to a key (using ver 2.69)
This is not available by default in preferences but you can add it manually. Open your user preferences and go to the Input tab, toggle 3D View and then Mesh.
Scroll to the bottom where you will see a button that says Add new. For the identifier, enter
wm.context_toggle and for the Context Attributes enter
space_data.use_occlude_geometry, next assign a key combination to it and save your user settings.
2.80 is still beta, but it doesn't hurt to know that for this advice to work is important to know that once you expand Mesh, you still need to expand the first entry too [Mesh (Global)]. Otherwise, you won't see that Add new button at the bottom.
Actually, after a closer inspection, the entries called "identifier", and "Context Attributes" are not found available.