mandatory property missing from MediaTrackConstraints

[jameshfisher]

Following desktopCapturer docs, I get type errors like:

error TS2322: Type '{ mandatory: { chromeMediaSource: string; chromeMediaSourceId: string; }; }' is not assignable to type 'boolean | MediaTrackConstraints | undefined'.
  Object literal may only specify known properties, and 'mandatory' does not exist in type 'MediaTrackConstraints'.

I've fixed this by adding:

interface MediaTrackConstraints {
    mandatory?: {
        chromeMediaSource: 'desktop',
        chromeMediaSourceId?: string,
    }
}

But I suspect this should be included in Electron's TypeScript defs.

(It actually looks like this API is part of Chrome rather than part of Electron, but then I'm not sure where Chrome-specific type defs should go.)

[jameshfisher]

Closing in favor of electron/electron#27139