My impression was that it had a faster Javascript engine, and it has spurred on other browsers. It's a market threat (users might switch), and an engineering goad (hey, it's possible - why can't you do it?) That serves Google's purpose as much as getting market share themselves.

Another aspect is blue sky: what webapps would become possible if the installed-based of javascript was an order of magnitude faster? What's good for webapps is good for google.