Spec appears to require gDM leak info on availability of audio

[eladalon1983]

The spec says as follows:

6. Let requestedMediaTypes be the set of media types in constraints with either a dictionary value or a value of true.

...

9. Run the following steps in parallel:
   1. For each media type T in requestedMediaTypes,
      1. If no sources of type T are available, reject p with a new DOMException object whose name attribute has the value NotFoundError.
      2. ...
      3. Prompt the user to choose a display device

This appears to require that if audio is requested by the application, and is not available for the user agent to share, then gDM should reject. (Note that this is done before prompting the user. It's not about what the user ultimately chooses.)

Presumably this was added for the perverse case of gDM called on a device with no attached screen and no visible screens, and where tab-capture was not yet supported?

Thanks @shangl for alerting me to this.

[alvestrand]

Should make it clear that requestedMediaTypes checked here is not meant to do audio.

[jan-ivar]

Should probably only be NotFoundError for video, since audio is optional (mentioned elsewhere in this spec)