The freezing in the artwork getter is broken

[bzbarsky]

In https://w3c.github.io/mediasession/#dom-mediametadata-artwork there is this step:

Call Object.freeze on image, to prevent accidental mutation by scripts.

But image is an IDL dictionary here, not a JS value, so you can't call Object.freeze on it.

Maybe this means to say that you convert the dictionary to a JS object, then freeze it? That would be a viable option if this is the defined behavior, but then the artwork attribute should return FrozenArray<object>, because when you're creating the FrozenArray it's done from a list of objects, not a list of MediaImage dictionaries.

[jan-ivar]

How does this spec imagine people change metadata? It would help if the examples showed this.

Here's what I get in Chrome:

navigator.mediaSession.metadata = new MediaMetadata({artist:"Ƭ̵̬̊", artwork:[{src:"A.png"}]})
navigator.mediaSession.metadata.artist = "Prince"
navigator.mediaSession.metadata.artwork[0].src = "B.png"
navigator.mediaSession.metadata.artist // Prince
navigator.mediaSession.metadata.artwork[0].src // "http://example.com/A.png"

artwork[0].src was not updated. That seems to spec and broken. How do I change artwork?

The other thing that's odd is there's no way to add or remove artwork. How do I do that?

If things are meant to be changed solely through the constructor, I'd make MediaImage an interface, and all attributes readonly.

[jan-ivar]

Or make MediaImage an interface and remove the freezing, and support

navigator.mediaSession.metadata.artwork[0].src = "B.png"

[ChunMinChang]

So there are two different issues here:

1. By the behavior defined in the current spec, the artwork in MediaMetadata must be FrozenArray<object> rather than FrozenArray<MediaImage>, so the item in the artwork can be frozen.
2. We probably should make MediaImage be an interface instead of dictionary

[youennf]

PR available at #343