Ubuntu – Immediately lock screen when I close laptop lid under Gnome 3 (14.04)

You're on the right track with logind.conf, but you only need to change this line from the default configuration:

HandleLidSwitch=ignore

(i.e. you don't need LidSwitchIgnoreInhibited=no).

In addition, you need to configure xfce4-power-manager to handle the lid switch. I found that the reliable way was to Quit it from the power manager icon menu before configuring it with

$ xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/logind-handle-lid-switch -s true

You'll then need to restart (unless there's another way to get logind to pick up its configuration, in which case I'd love to hear it!).

After this, the lid switch should operate according to the settings in the power manager.

I found this solution thanks to a comment on a bug linked by a helpful person in #xubuntu.

Note that this breaks screen locking on suspend.