Each part of Android ecosystem works together to build a strong defense that run smoothly and effectively. Google work with 30 to 50 teams outside android security team to secure the Android.
Defend against internet-borne threat. Anything deals with security of application which belong or not belong to the Play-Store.
Teams like malware analysis team, malware research team, Unwanted behavior analysis team, Google play policy detection and so on work on this target.
Google work on security of OS and device to make platform safer. Some teams like Cryptography team, Trusted execution environment team and so on works on this target.
This area is for how to securely develop android applications. For example how to make sure only safe code goes to apps in the first place. And how to manage vulnerabilities and patch system.
Security Enhancements | Android Open Source Project

Note
<aside> 💡 Google believes malware protection should be built-in to the OS
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