Cruise, the self-driving car arm of General Motors, has an unexpected new ally in its bid to keep its corporate master at the forefront of an industry enduring its greatest period of change in generations: Honda. In a deal announced today, the Japanese automaker will help San Francisco-based Cruise and its Detroit owner develop and mass produce a new sort vehicle for a world in which human drivers are no longer needed. Honda is opening its checkbook too, pledging to spend $2 billion on the project over 12 years, and immediately putting a $750 million equity investment into Cruise. For Honda, the partnership offers entree into a self-driving space where it has thus far spent little time and effort. For Cruise and GM, the newcomer adds engineering know-how, especially with regard to interior design.