XRViews should be marked as inactive after the frame that produced them ends

[cabanier]

With the addition of the first person observer, some views might always be in the current list of views.
Currently, there's is no checking to see if the XRView was from a previous frame but no longer in the list of views. Should this be added to the getViewPort algorithm?

[toji]

The https://immersive-web.github.io/webxr/#dom-xrwebgllayer-getviewport algorithm does currently check to ensure that the XRFrame which produced the XRView is valid:

1. Let frame be view’s frame.
2. ...
3. If frame’s active boolean is false, throw an InvalidStateError and abort these steps.

So that's been covered previously. However, I think that this pattern breaks down now that #1088 has landed, in that the same XRFrame object is able to be re-used every frame. As a result we'll want to update this to have each XRView track its own "active" state.

[cabanier]

@toji Should I close this one and let you open another issue to move the active boolean to the view?
This will also cause changes in the WebXR Layers spec.

[toji]

No need for a new issue. I just changed the title of this one to better reflect what needs to happen.

[Manishearth]

I suspect this can be fixed with the same stuff that fixes #1090 , if done right

[Manishearth]

I'll take a crack at both these issues