Remove prefixed Shadow DOM APIs in Element.

PerformanceTests/ShadowDOM/ShadowReprojection.html

Index: PerformanceTests/ShadowDOM/ShadowReprojection.html
diff --git a/PerformanceTests/ShadowDOM/ShadowReprojection.html b/PerformanceTests/ShadowDOM/ShadowReprojection.html
index 19b5a0b171786938f9b09ce86aa791369868cbcc..798d805aee9a834712c18e6549d7a07d1f7aec36 100644
--- a/PerformanceTests/ShadowDOM/ShadowReprojection.html
+++ b/PerformanceTests/ShadowDOM/ShadowReprojection.html
@@ -25,11 +25,11 @@ function setup()
         host.appendChild(div);
     }
 
-    var shadowRoot = host.webkitCreateShadowRoot();
+    var shadowRoot = host.createShadowRoot();
     shadowRoot.innerHTML = '<div id="host2"><shadow><content></content></shadow></div>';
 
     var host2 = shadowRoot.getElementById('host2');
-    var shadowRoot2 = host2.webkitCreateShadowRoot();
+    var shadowRoot2 = host2.createShadowRoot();
     shadowRoot2.innerHTML = '<content select=".selected"></content>';
 }