Revert of Re-landing r170008, removing prefixed Shadow DOM APIs in Element.

PerformanceTests/Events/EventsDispatchingInShadowTrees.html

Index: PerformanceTests/Events/EventsDispatchingInShadowTrees.html
diff --git a/PerformanceTests/Events/EventsDispatchingInShadowTrees.html b/PerformanceTests/Events/EventsDispatchingInShadowTrees.html
index 3b42efaedf24870bbd468fb347c0feb58e832ed5..01eaeb68617b49a3b76837298fc4210ca184ae96 100644
--- a/PerformanceTests/Events/EventsDispatchingInShadowTrees.html
+++ b/PerformanceTests/Events/EventsDispatchingInShadowTrees.html
@@ -20,7 +20,7 @@
     for (i = 0; i < branch; ++i) {
         var child = document.createElement('div');
         node.appendChild(child);
-        var shadowRoot = child.createShadowRoot();
+        var shadowRoot = child.webkitCreateShadowRoot();
         createTreeOfTrees(shadowRoot, depth - 1, branch, eachTreeHeight);
     }
 }