The combined pass is built with the contributions the user finds fit.
It is useful for lightmap baking, as well as non-view dependent effects
baking.
The manual will be updated once we get closer to the 2.77 release.
Meanwhile the new page can be found here:
http://dalaifelinto.com/blender-manual/render/cycles/baking.html
Reviewers: sergey, brecht
Differential Revision: https://developer.blender.org/D1674
9a76354585