/usr/share/gnome/wm-properties/openbox.desktop is in openbox-gnome-session 3.5.2-8+deb8u1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | [Desktop Entry]
Type=Application
Name=Openbox
Exec=openbox
Type=Application
Categories=System;
# name we put on the WM spec check window
X-GNOME-WMName=Openbox
X-GNOME-Provides=windowmanager
NoDisplay=true
# our config tool
ConfigExec=obconf
[Window Manager]
SessionManaged=true
|