what is online ad networks for $100, alex

I don't know why this is being downvoted. This is called malvertising and its one of the most significant vectors for exploiting a vulnerability like this. Its happened multiple times over the last two decades.

My read of Google's disclosure is that there is likely no known escape from the sandbox. I don't agree this would be reported this way just because "user action" like "using web browser" is required. Even if this individual CVE is correctly an 8.8 there would be a critical assessment of a known chain. The only reason there wouldn't be, would be if the other vulnerability is known to Google but has no patch yet.