[webcomponents] Shadow DOM and "insertion steps" / "removing steps" (#438)

The Shadow DOM specification needs to "monkey patch" DOM Standard's "insert" and "remove" algorithms to account for shadow trees.

If nodes in shadow trees are never notified they have been inserted or removed, there are no hooks for other standards to define how they should behave there.

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/438