In its services and repair terms and conditions, Google says it will keep devices sent in for repair if they have a non-OEM part.
Update:
Google changes repair policy after criticism of third-party parts ban Google previously said it would not return mailed-in devices using “unauthorized” parts.
This one isn’t though. There’s no law against it in the United States, thus it is legal.
Murder contracts specifically are illegal because they contract for an illegal activity. Giving your phone to Google isn’t an illegal activity. Yes, it sounds and feels like theft, but it doesn’t meet the legal definition of theft.