[mcpherrinm]

The "marketing budget for Chrome" is something thrown around internally at Mozilla, but that number was pulled out of calculations on how much it would cost somebody else to advertise Chrome that google does on its own properties. Google does not have to charge itself to advertise itself.

[deciplex]

They have to give up the revenue advertising for someone else, to advertise for themselves.

[tempestn]

In theory; in practice most of the places where Chrome is advertised they wouldn't advertise a third-party product. (Like on the Google search engine homepage, for instance.) That said, I suppose they could be advertising a different internal product there, so there's certainly an opportunity cost regardless.