Earlier quoted context omitted.
Very little development in Google3 happens locally. You aren't even allowed to keep the source code on your local disk, and this is true no matter what OS it runs. (Android and Chromium are different though.) You have access to an extremely powerful remote workstation that from a UI perspective functions almost identically to a local workstation, via Chrome Remote Desktop. Plus, no one builds things locally, even on…
I can understand Android (including the Linux kernel) being "too big" and "too separate" to go into Google3, but why Chromium? When it was forked from KHTML/WebKit it was probably not that big compared to the rest of Google's codebase.
Size has nothing to do with it.