I don't think Google's primary goal here is to have the largest market share in the browser market but to be able to drive innovation in the other leading browsers through competition. Google Chrome drove Firefox (and others) to improve the speed of their javascript engines/interpreters which is hugely beneficial for Google meaning their web apps now run faster across the board. In my opinion, Google Chrome exists to…
If they wanted to make the web better, why didn't they just contribute to the Firefox project itself rather than inventing their own browser?
Releasing, yet another browser only complicates things for existing web developers.