The tether service's GetTetherTechnologyState method (https://cs.chromium.org/chromium/src/chrome/browser/chromeos/tether/tether_service.cc?type=cs&q=%22GetTetherTechnologyState()+%7B%22+f:tether_service.cc$&g=0&l=478) will return the technology state chromeos::NetworkStateHandler::TechnologyState::TECHNOLOGY_UNAVAILABLE in the edge case of a device with cellular and tethering when the cellular pref is off because the cellular pref controls Instant Tether when both are present. This is a little deceptive because tethering can be re-enabled in this case with a pref change, while the rest of the situations that return TECHNOLOGY_UNAVAILABLE cause the Instant tether feature not to appear at all in the Settings MultiDevice subpage.

We should probably handle this case more like the case when instant tethering is turned off by the pref, however it's a pretty rare edge case and the consequence of mishandling it (i.e. the subpage doesn't show the tether feature) isn't disastrous, it's not top priority.