Nov. 9 (Bloomberg)—Google Inc., owner of the world’s most popular Internet search engine, agreed to pay $750 million in stock for AdMob Inc., a mobile-phone advertising startup backed by Google investor Sequoia Capital.The deal shores up Google’s position in the mobile- advertising market, helping decrease its reliance on desktop Internet ads, where growth is slowing. AdMob, which sells ads displayed on wireless devices, has benefited from the popularity of smart phones, such as Apple Inc.’s iPhone and Research In....