It is the original function for 12.04, but it does not work in my computer, maybe as I use the compiz config settings manager, so there are some conflicts. What can I do to fix it? There are too many parameters in the CCSM, wish you help.
I suggest to have a look at this question to learn how to reset Compiz' settings.
If you don't want to mess up your Compiz settings in future, use MyUnity instead of CompizConfig Settings Manager. There are less options, but it is safe to use them.
I found that the Unity function to show all windows for an App fails if Chrome is currently showing any notifications (e.g. calendar notifications in the bottom-right of the screen). If I delete all my notifications then the function works correctly.
Hopefully Unity will fix this bug in due course, but in the mean time, closing notifications seems to do the trick at least for me.