Revert of Remove prefixed Shadow DOM APIs in Element.

Source/core/dom/Element.idl

Index: Source/core/dom/Element.idl
diff --git a/Source/core/dom/Element.idl b/Source/core/dom/Element.idl
index 4d9f75fb419f2fdcdc56a58df7385319a0bdb21f..229349dd18b06afad935efc8eaccb51610cf35df 100644
--- a/Source/core/dom/Element.idl
+++ b/Source/core/dom/Element.idl
@@ -116,6 +116,10 @@
     [PerWorldBindings] readonly attribute ShadowRoot shadowRoot;
     [PerWorldBindings] NodeList getDestinationInsertionPoints();
 
+    // To-be-deprecated prefixed Shadow DOM API
+    [ImplementedAs=createShadowRoot, RaisesException, MeasureAs=ShadowDOMPrefixedCreateShadowRoot] ShadowRoot webkitCreateShadowRoot();
+    [ImplementedAs=shadowRoot, PerWorldBindings, MeasureAs=ShadowDOMPrefixedShadowRoot] readonly attribute ShadowRoot webkitShadowRoot;
+
     // CSSOM View Module API
     ClientRectList getClientRects();
     ClientRect getBoundingClientRect();