[mediacapture-main] Clarify whether groupId is origin-unique

jyasskin has just created a new issue for 
https://github.com/w3c/mediacapture-main:

== Clarify whether groupId is origin-unique ==
In #202, @jan-ivar pointed out that 
[`MediaDeviceInfo.groupId`](https://w3c.github.io/mediacapture-main/#widl-MediaDeviceInfo-groupId)
 isn't explicitly specified to be origin-unique. However, the 
[`enumerateDevices`](https://w3c.github.io/mediacapture-main/#widl-MediaDevices-enumerateDevices-Promise-sequence-MediaDeviceInfo)
 algorithm sets `groupId` to "a newly generated unique identifier" if 
no device in _oldList_ is in the same physical device. I believe that 
has to be origin-scoped in order for `deviceId` to be origin-scoped.

_oldList_ is bound by
> If this method has been called previously within this browsing 
session, let oldList be the list of MediaDeviceInfo objects that was 
produced at that call (resultList); otherwise, let oldList be an empty
 list.

And then objects from it are used to populate the return value of 
`enumerateDevices()`:
> If device is represented by a MediaDeviceInfo object in oldList, 
append that object to resultList...

That's a little confused: If the method was called in a different 
execution context in the same browsing session, this returns a 
MediaDeviceInfo object from a different global object, so `instanceof`
 checks won't work. But you can't just limit to previous calls in the 
current execution context or `groupId` won't be shared within the 
origin.

See https://github.com/w3c/mediacapture-main/issues/222

Received on Tuesday, 28 July 2015 19:07:38 UTC