Endpoint for auto-replies of authorization prompt dialogs

[javifernandez]

This new endpoint would have the purpose of handling the prompt dialog launched to ask the user for confirmation after a request of the registerProtocolHandler method. This is specified in the Custom Handler specification as follows:

A user agent could, for instance, prompt the user and offer the user the opportunity to add the site to a shortlist of handlers, or make the handlers their default, or cancel the request. User agents could also silently collect the information, providing it only when relevant to the user.

The request of a new endopoint has been suggested in a wpt related issue as a way to to avoid launching the prompt dialog, assuming some kind of auto-reply functionality.

Inspiration can be taken from:
https://w3c.github.io/permissions/#automation

In the case of the SetPermission extension command, it requires a PermissionDescriptor as an input argument. I've suggested to add a new descriptor for the Custom Handler spec, so that we could use this exception command. However, this proposal has been rejected clearly.

[whimboo]

@AutomatedTester dupe of #385?

[javifernandez]

I've filed an issue for the html spec to define a new extension command in the Custom Handlers section, so that we could handler automatically the prompt dialogs potentially launched by the registerProtocolHandler method.

We could close this issue if we finally implement such new WebDriver endpoint.

[javifernandez]

We have implemented our new endpoont in the HTML spec so at least for that case, we don't need this issue anymore. Reopen if needed.