Implement Custom Elements' attributeChangedCallback.

LayoutTests/fast/dom/custom/registration-context-delete-during-attribute-changed-retrieval.html

Index: LayoutTests/fast/dom/custom/registration-context-delete-during-attribute-changed-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-attribute-changed-retrieval.html
similarity index 88%
copy from LayoutTests/fast/dom/custom/registration-context-delete-during-register-created-retrieval.html
copy to LayoutTests/fast/dom/custom/registration-context-delete-during-attribute-changed-retrieval.html
index 651466f5626273bae820bda97931d716a81574a8..59d5b6a8fac0741df296c57ec1408499181f4008 100644
--- a/LayoutTests/fast/dom/custom/registration-context-delete-during-register-created-retrieval.html
+++ b/LayoutTests/fast/dom/custom/registration-context-delete-during-attribute-changed-retrieval.html
@@ -5,14 +5,14 @@
 <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 attributeChanged callback is retrieved.');
     jsTestIsAsync = true;
     successfullyParsed = true;
 } else {
     // The child frame
 
     var proto = Object.create(HTMLElement.prototype, {
-        createdCallback: {
+        attributeChangedCallback: {
             get: function () {
                 destroyContext();
                 return function () { }