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 72%
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..4c38a97d53014f9d7bb240ce22f2f5f7be91fba2 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
@@ -5,23 +5,24 @@
 <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\'s constructor property is retrieved.');
     jsTestIsAsync = true;
     successfullyParsed = true;
 } else {
     // The child frame
-
     var proto = Object.create(HTMLElement.prototype, {
-        createdCallback: {
+        constructor: {
+            configurable: true,
             get: function () {
                 destroyContext();
-                return function () { }
+                return HTMLElement;
             }
         }
     });
 
     try {
-        document.registerElement('x-a', {prototype: proto});
+        var element = document.registerElement('x-a', {prototype: proto});
         log('FAIL expected register to throw an exception');
     } catch (ex) {
         log('PASS caught expected exception "' + ex + '"');