We are hosting git repo on the google cloud platform. I know for github.com, we can use pull requests for code reviews, but google cloud does not seem to provide that.
How do I perform code review for repos on google cloud platform?
One possibility (not ideal, I know, but still something) would be to have your cloud repo connected to a GitHub or BitBucket repo which you could use for code reviews instead. From Connecting a Hosted Repository:
You can connect a Cloud Source Repository to a Git repository hosted on GitHub or Bitbucket. When you push changes to the hosted repository, the changes are automatically synchronized with the Cloud Source Repository.