Apple cooperates within WebKit well with WebKitGtk. They supported LLVM when it is in their interest.
Chrome is used as proprietary web-engine to vendor lock-in the web. While often used by others, I’m not aware of a broad cooperation. Android is a shadow of Linux, merely using the Linux-Kernel, not GNU. Plus a lot of closed-source code (PlayServices, App Signatures, Google Cloud, Google Apps).
Googles open-source projects seem often exclusive Google only projects? Google works together with others! But especially Chrome and AOSP are…causing worries.