I seriously doubt that Google doesn't care about market share for this thing that they've invested in. Strategically, what good is advancing the state of the art in browsers if people don't migrate to it?
Expanding on this a bit: we all know and love Google, but its a business, and one that basically supports the existence of another browser by paying to be the default search engine used in one of that browser's interface widgets. It's not an insignificant amount, either (http://news.cnet.com/8301-10784_3-9804156-7.html); there's no way they paid that much to develop Chrome. Keep that money in house, make the shareholders happy; keep Chrome open source, keep the hackers happy. Why wouldn't they want users to start adopting Chrome instead of FF?
I'm sure that the Chrome team would be absolutely stoked to have a lot of users, but strategically, it simply doesn't matter. The goal here is to advance the state of the art in browsers. Performance, stability, and security (in terms of process isolation) were and still are lacking in all other browsers compared to Chrome. This is very much about pushing the state of the web, not about gaining market share. Google Chrome delivers in this regards.