[webcomponents] MutationObserver and attachShadow() (#390)

I'm looking for a way to keep track of ShadowRoots being created. Neither does the current implementation of ShadowDOM/MutationObserver in Firefox 44 and Chrome 48 register a mutation for `element.createShadowRoot()` (renamed to `attachShadow()`), nor does either specification mention this situation specifically.

To the best of my knowledge it is currently not possible to get identified when a ShadowRoot is created for an element.

(originally raised at whatwg/dom#170)

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/390