[mediacapture-record] Error member in an Event for runtime-errors is a bad idea

jan-ivar has just created a new issue for 
https://github.com/w3c/mediacapture-record:

== Error member in an Event for runtime-errors is a bad idea ==
...because the `Error`'s file, line number and stack will always be 
empty.

Not only is this wasteful, it fools people into thinking it *might* 
have useful information that they better log or forward, taking the 
place of more useful information.

Here's an [example](https://jsfiddle.net/tmwLxjLy/) (yes I like 
promises, and yes the example is mediaRecorder,  but it has the same 
event):

```js
var rec = new MediaRecorder(stream);
rec.start();
var stopped = new Promise((resolve, reject) => {
  rec.onstop = resolve;
  rec.onerror = event => reject(event.error));
});
```
`stopped` resolves when the recording ends, or rejects at the first 
runtime error, whichever happens first.

But when a `SecurityError` error later shows up in my console, there's
 no file or line number. In a larger program, this would suck.

If we replace `.error` with `.name` and `.message` then I know there's
 no deeper information to forward:

    rec.onerror = event => reject(new DOMException(event.message, 
event.name));

And now the `SecurityError` points to this call site, which tells me 
it's a runtime error in `rec`.

I think this is a general problem with all runtime-error events.

Please view or discuss this issue at 
https://github.com/w3c/mediacapture-record/issues/53 using your GitHub
 account