Webrtc-pc: Make RTCError inherit from DOMException?

[alvestrand]

According to @domenic it is now possible to define IDL types that inherit from DOMException.
This would allow us to do a pure IDL specification of RTCError, which is a far simpler specification than the one we're doing now (and comports with the one in-progress implementation I know about).

DOMException spec:
https://heycam.github.io/webidl/#idl-DOMException

Should we do this?

[henbos]

This would also be a lot simpler to implement (I'll update my CL to verify). The RTCError is not implemented by any browser yet and in my intent to implement & ship we got pushback.

Should we do this? I think so.

[foolip]

This is great if possible. One thing that needs to be decided is what new RTCError().code should return, probably zero.

[henbos]

Implementing RTCError to extend DOMException in chromium was trivial.