When Comcast announced its planned $45 billion merger with Time Warner Thursday, the company cited the emergence of a new competitor as one reason that regulators should approve the deal: Google. But some are questioning whether Googles new ultra-fast Internet service, Google Fiber, presents enough of a challenge to justify dramatically increasing Comcasts market power. In a blog post, Comcast Executive Vice President David L. Cohen cited Googles new role as an Internet provider as one reason why Comcast could not become too dominant. …