You don't need implementation in the browser. You need the CAs to provide the public audit logs and all HTTPS domain owners to check them for unexpected issuance.
The browser is just a political tool to enforce the CAs to provide the logs, for example by no longer marking their certs as trusted unless they do so.
There is none, which is why I said the browser is just a tool in a politics game. It enforces the existence of the log. The security doesn't come from checking whether the cert is in the log!
Not hard to see why from your explanation.
You don't need implementation in the browser. You need the CAs to provide the public audit logs and all HTTPS domain owners to check them for unexpected issuance.
The browser is just a political tool to enforce the CAs to provide the logs, for example by no longer marking their certs as trusted unless they do so.