Google may be motivated to attempt things like Dart and NaCl which help drive forward their own products first and foremost, but they have a consistent reputation of making their web-advancing client-side technologies open source too (Dart, NaCl, WebM, SPDY, Chromium, Webkit, etc are all open source). They also have Mozilla, Opera and Apple pushing forwards as well (though I'd argue that IE9/10 isn't putting much competitive pressure on anyone).

If Chrome is abandoned by Google you're free to fork Chromium, acquire licenses for it's restricted plugins and it'll only slow the web's march forward, not actively hinder it. It's entirely possible for another group to carry the Chromium torch, and Google/Chrome has never yet intentionally damaged the quality of standards-compliant competing web products (though they don't offer quirks-mode fixes for crap tailored only to IE).

> The best case scenario is a better internet, but only for google products for them.

Google operates a search engine, meaning most of the time it points people to other websites. Many of these sites are not under Google's control, but many of them run AdSense. The more pages you visit, the more ads you see. If the internet gets generally faster, Google sites or not, that works in their favor.