Use window.WebKitShadowRoot for checking whether a node is shadow root or not.
https://bugs.webkit.org/show_bug.cgi?id=88748

Reviewed by Hajime Morita.

* fast/dom/shadow/resources/shadow-dom.js:
(isShadowRoot):
Modified to use window.WebKitShadowRoot instead of node name.
* resources/dump-as-markup.js:
(Markup.get var):
Added shadowRootList which has information about whether the given node
is a shadow root or not.
(Markup):
(Markup._get):
If the given element is a document fragment and its address is in
shadowRootList, use "<shadow:root>".
(Markup._getShadowHostIfPossible):
Only this method uses internals.shadowRoot and obtains the youngest
shadow root from the given node. So update shadowRootList in this
method.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@139169 268f45cc-cd09-0410-ab3c-d52691b4dbfc