support/fix window.frames

[sigmundch]

window.frames currently returns the same instance window. In JS this works because the window is also an array that contains all the child frames.

This doesn't work in Dart because [] and .length are not supported on the returned type. We should probably update the return type to be more sensible (e.g. List<Window> get frames())

We can work around this for now to get frames by doing
window.queryAll('iframe')
and retrieving the window from the iframe element.

Fixing widnow.frames will still be important long term if we want to support accessing an grandchild-iframe (e.g. window.frames[0].frames[1]). This is because the window returned by the iframe element is more restricted and doesn't allow accessing its document content (e.g. the following is illegal: window.queryAll('iframe')[0].queryAll('iframe')[1])

[vsmenon]

Removed Area-UI label.
Added Area-DOM label.

[vsmenon]

Set owner to @vsmenon.
Added this to the M1 milestone.

[iposva-google]

Removed Area-DOM label.
Added Area-HTML label.

[vsmenon]

We've decided to remove window.frames as it no longer appear to be commonly used - it's currently broken.

The workaround should work for common cases:

window.queryAll('iframe').map((f) => f.contentWindow);

Please star if you'd like to see this added.

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cc @blois.
cc @sigmundch.
Removed this from the M1 milestone.
Added this to the Later milestone.
Removed Type-Defect label.
Added Type-Enhancement label.

[vsmenon]

Removed the owner.

[efortuna]

Added html-api label.

[blois]

Fixed as this API has been removed.

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Added Fixed label.