Implement Custom Element's class side inheritance

LayoutTests/fast/dom/custom/registration-context-delete-during-register-base-constructor-retrieval.html

Index: LayoutTests/fast/dom/custom/registration-context-delete-during-register-base-constructor-retrieval.html
diff --git a/LayoutTests/fast/dom/custom/registration-context-delete-during-register-created-retrieval.html b/LayoutTests/fast/dom/custom/registration-context-delete-during-register-base-constructor-retrieval.html
similarity index 84%
copy from LayoutTests/fast/dom/custom/registration-context-delete-during-register-created-retrieval.html
copy to LayoutTests/fast/dom/custom/registration-context-delete-during-register-base-constructor-retrieval.html
index 488859fae9f62d83304976652cb1a85cf1c8a522..eb6096e0562fee182e255f127409d4ef1b52341e 100644
--- a/LayoutTests/fast/dom/custom/registration-context-delete-during-register-created-retrieval.html
+++ b/LayoutTests/fast/dom/custom/registration-context-delete-during-register-base-constructor-retrieval.html
@@ -5,17 +5,17 @@
 <script>
 if (fork()) {
     // The controlling parent frame
-    description('Tests destroying a context during registration at the point when the created callback is retrieved.');
+    description('Tests destroying a context during registration at the point when the prototype constructor prototype is retrieved.');
     jsTestIsAsync = true;
     successfullyParsed = true;
 } else {
     // The child frame
 
     var proto = Object.create(HTMLElement.prototype, {
-        createdCallback: {
+        constructor: {
             get: function () {
                 destroyContext();
-                return function () { }
+                return HTMLElement;
             }
         }
     });