Contributions to this project must be accompanied by a Contributor License Agreement (CLA). You (or your employer) retain the copyright to your contribution; this simply gives us permission to use and redistribute your contributions as part of the project.
If you or your current employer have already signed the Google CLA (even if it was for a different project), you probably don't need to do it again.
Visit https://cla.developers.google.com/ to see your current agreements or to sign a new one.