As far as I can tell, GNOME3 does not have a DPI setting anymore. Instead, you must use
dconf-editor to change the following key (I found it by looking/searching through dconf-editor):
Code:
/org/gnome/desktop/interface/text-scaling-factor
I hope there's going to be some sort of user interface to replace the missing "Appearance" panel for gnome-control-center and provide an easier/more discoverable way to set this property...