It doesn't, that's Android Webview which is distributed separately. It may however bundle its own instance of the Chrome networking library which is a few MB itself.
For apps like Gmail and a handful of others, they are big enough that they need multiple layers of fallback. e.g. they can't just use a networking layer, they need a fallback separate implementation in case that breaks, so that they can recover. They might have 2 or even 3 options for some of the critical parts, all so that if stuff goes wrong they can as close to guarantee recovery as they can get.
Mobile is quite specific in this regard, because you don't have hardware access, network is heavily restricted, battery reduces the amount you can do, etc.
For apps like Gmail and a handful of others, they are big enough that they need multiple layers of fallback. e.g. they can't just use a networking layer, they need a fallback separate implementation in case that breaks, so that they can recover. They might have 2 or even 3 options for some of the critical parts, all so that if stuff goes wrong they can as close to guarantee recovery as they can get.
Mobile is quite specific in this regard, because you don't have hardware access, network is heavily restricted, battery reduces the amount you can do, etc.
Source: I work on mobile SRE things at Google.