Code review comment for lp:~mir-team/mir/cursor-spike-phase-4-implement-api

could be private:
405 + mi::CursorController* const cursor_controller;
406 +
407 + std::mutex surface_observers_guard;
408 + std::map<ms::Surface*, std::weak_ptr<ms::SurfaceObserver>> surface_observers;

should guard against exceptions:
441 +mi::CursorController::~CursorController()
442 +{
443 + input_targets->remove_observer(observer);
444 +}

needed?
484 + assert(input_targets);