Google Inc. plans to make its self-driving cars unit, which will offer rides for hire, a stand-alone business under the Alphabet Inc. corporate umbrella next year, a person briefed on the company’s strategy said. In August, the Mountain View, California-based company reorganized itself into a conglomerate called Alphabet. The company said it plans to spin out several of its advanced-technology units into stand-alone companies within the Alphabet portfolio, including its robotics division, its health-care company Verily, the Google Ventures and Google Capital investment firms, Google Inc., the search-engine company, and Nest, which produces intelligent smoke alarms and thermostats. The self-driving car unit now resides in the research division called Google X.