Alphabet Inc. and Fiat Chrysler Automobiles NV are doubling down on their self-driving partnership, adding about 100 more Pacifica Hybrid minivans to an autonomous fleet first announced in May, according to people familiar with the decision. Last month, the two companies announced the production of the initial 100 minivans, vehicles equipped with the technology developed by Waymo, the new Alphabet company formed from its Google car project.