My point was Google didn't pay anything to gain the market share because they advertise Chrome on their frontpage, something neither Firefox, nor IE, nor Opera nor Safari, nor anyone else in that matter could do.

From an antitrust law point of view, using your monopoly status in one area as a weapon against the competition in other areas is something that likely gets you in trouble.

Although, it helps to remember that in the EU, you don't need nearly as big a market share before their competition law kicks in and places restrictions on your behavior, so things that you can still get away with in the US can be quite illegal in the EU.

They paid to have it bundled as a drive-by install in other popular software, spyware-style.