Spin-off from the discussion on crbug.com/765923.

Some new APIs should not be exposed in WebView (e.g. if they are not working or go against WebView workflow). A recent example is the WebShare API (crbug.com/765923).

We currently do have a 'test' which lists newly exposed interfaces. It is a non-failing test because in the past it involved too many rebaselines and attention from the sheriff. Most of the newly exposed interfaces are usually OK to go in WebView.

At present we don't have an automatic signaling/monitoring system or well-defined process to escalate such regressions. Hence this bug to investigate and set-up a more waterproof system for handling and resolving such issues.