Contributions to any Google project must be accompanied by a Contributor License Agreement. This is not a copyright assignment, it simply gives Google permission to use and redistribute your contributions as part of the project.
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If you are an individual writing original source code and you're sure you own the intellectual property, then you'll need to sign an individual CLA.
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If you work for a company that wants to allow you to contribute your work, then you'll need to sign a corporate CLA.
You generally only need to submit a CLA once, so if you've already submitted one (even if it was for a different project), you probably don't need to do it again.