Generally branching isn't really a thing at Google. Work is done at the code review level per change list ("CL"). Most changes happen through incremental submission of reviewed CLs, not by merging in feature branches. Every CL must run the gauntlet of code review, as well as can not usually be submitted without passing tests. There are rare cases where branching is used, but not commonly.

As for notifications, the CL has a list of reviewers and subscribers. If you want to see code changing, you watch those CLs. Most projects have a list where all submitted CLs go.