Leadership. Google looks for a particular type of leadership called “emergent leadership.” You'll typically be working in cross-functional teams at Google, and different team members are expected to step up and lead at different times in the lifecycle of a project when their skills are needed.
Googleyness (i.e. culture fit). The company wants to make sure Google is the right environment for you. Your interviewer will check whether you naturally exhibit the company's values including: being comfortable with ambiguity, having a bias to action, and a collaborative nature.