This is for contributors outside of Google.

I don't know why this is needed, but glancing at the CLA the clause which is most obviously not covered by the Apache license is this one:

"You represent that you are legally entitled to grant the above license. If your employer(s) has rights to intellectual property that you create that includes your Contributions, you represent that you have received permission to make Contributions on behalf of that employer, that your employer has waived such rights for your Contributions to Google, or that your employer has executed a separate Corporate CLA with Google."

Linux requires a similar declaration to accept code, but many free software projects do not, and it's not a part of any of the usual licenses.