Remove dom.webcomponents.shadowdom.enabled.
Remove dom.webcomponents.shadowdom.enabled.

This patch removes the dom.webcomponents.shadowdom.enabled pref and all its
references, including the following functions:

* nsContentUtils::IsShadowDOMEnabled()
* nsIDocument::IsShadowDOMEnabled()
* nsDocument::IsShadowDOMEnabled(JSContext* aCx, JSObject* aGlobal)
* nsDocument::IsShadowDOMEnabled(const nsINode* aNode)
* nsTextNode::IsShadowDOMEnabled(JSContext* aCx, JSObject* aObject)

This function is renamed and updated to nsDocument::IsCallerChromeOrAddon():

* nsDocument::IsShadowDOMEnabledAndCallerIsChromeOrAddon(JSContext* aCx, JSObject* aObject)

I didn't change the tests that load Shadow DOM tests in an iframe, in the interest of keeping hg annotation history.

Differential Revision: https://phabricator.services.mozilla.com/D11183

saneyuki/servo,notriddle/servo,paulrouget/servo,szeged/servo,DominoTree/servo,saneyuki/servo,DominoTree/servo,notriddle/servo,notriddle/servo,emilio/servo,nnethercote/servo,splav/servo,larsbergstrom/servo,szeged/servo,pyfisch/servo,pyfisch/servo,larsbergstrom/servo,nnethercote/servo,splav/servo,splav/servo,notriddle/servo,paulrouget/servo,larsbergstrom/servo,KiChjang/servo,peterjoel/servo,KiChjang/servo,nnethercote/servo,DominoTree/servo,emilio/servo,splav/servo,peterjoel/servo,paulrouget/servo,emilio/servo,saneyuki/servo,szeged/servo,larsbergstrom/servo,paulrouget/servo,szeged/servo,peterjoel/servo,larsbergstrom/servo,DominoTree/servo,pyfisch/servo,szeged/servo,nnethercote/servo,larsbergstrom/servo,nnethercote/servo,notriddle/servo,paulrouget/servo,peterjoel/servo,larsbergstrom/servo,splav/servo,notriddle/servo,KiChjang/servo,nnethercote/servo,KiChjang/servo,larsbergstrom/servo,splav/servo,saneyuki/servo,KiChjang/servo,paulrouget/servo,KiChjang/servo,pyfisch/servo,emilio/servo,peterjoel/servo,paulrouget/servo,peterjoel/servo,paulrouget/servo,pyfisch/servo,notriddle/servo,szeged/servo,KiChjang/servo,KiChjang/servo,DominoTree/servo,szeged/servo,larsbergstrom/servo,emilio/servo,splav/servo,larsbergstrom/servo,paulrouget/servo,pyfisch/servo,splav/servo,splav/servo,splav/servo,saneyuki/servo,nnethercote/servo,DominoTree/servo,peterjoel/servo,saneyuki/servo,pyfisch/servo,notriddle/servo,emilio/servo,pyfisch/servo,szeged/servo,peterjoel/servo,DominoTree/servo,saneyuki/servo,peterjoel/servo,saneyuki/servo,nnethercote/servo,paulrouget/servo,saneyuki/servo,emilio/servo,emilio/servo,DominoTree/servo,szeged/servo,szeged/servo,pyfisch/servo,notriddle/servo,emilio/servo,notriddle/servo,peterjoel/servo,emilio/servo,DominoTree/servo,saneyuki/servo,pyfisch/servo,nnethercote/servo,DominoTree/servo,KiChjang/servo,nnethercote/servo,KiChjang/servo