And even if it were, surely they wouldn't be locked to the same version as Chrome or Android?

Basically, I think lmm and gecko are both right: there should be exactly one repository per project, where a project is defined in terms of a set of stable interfaces with the outside world. Whether the total set of stuff your company is doing should be one project or a few or many, depends on the nature of the stuff you do, what it has to deal with, and your company structure; but the answer to that should determine your repository structure.