Google is weighing an investment in a new, multimillion-dollar cable across the Pacific Ocean, people familiar with the matter said, a move that comes as big technology companies send an increasing amount of traffic across private networks. The prospective investment illustrates a counterintuitive trend in telecom amid debates about equal access to the Internet: Software companies like Google and Facebook, which were born on the Web, are becoming responsible for the lion’s share of the growth taking place outside of it. The shift gives the companies more control over quality and prioritization of their traffic long before it reaches consumers. The search giant would control its own portion of the new subsea cable and use it to connect data centers in Oregon and elsewhere with Japan, according to two people familiar with its plans.