Google Inc., which is facing an antitrust inquiry into its purchase of online advertising company DoubleClick Inc., on Friday pointed to a string of related acquisitions by competitors as evidence of what it sees as a healthy market that doesn't require government intervention. Google policy counsel Pablo Chavez said in a blog post that acquisitions such as Microsoft Corp.'s purchase of AdECN Inc., announced Thursday, mean "that the leading Internet companies believe that they can position themselves to succeed in the online advertising space