Add assert that updateLayoutTree clears dirty bits.

LayoutTests/fast/parser/append-child-followed-by-document-write.html

Index: LayoutTests/fast/parser/append-child-followed-by-document-write.html
diff --git a/LayoutTests/fast/parser/append-child-followed-by-document-write.html b/LayoutTests/fast/parser/append-child-followed-by-document-write.html
index 01698785f46101c0a9d5324e0f8d401c5aeaaecd..c3d9c5e97b6c3cf1f18b87f1de3056e1e60c736b 100644
--- a/LayoutTests/fast/parser/append-child-followed-by-document-write.html
+++ b/LayoutTests/fast/parser/append-child-followed-by-document-write.html
@@ -8,12 +8,11 @@ function go() {
 
   // Ideally we would use the dump-as-markup test framework for this test, but
   // the contortions we go through here are too tricky for dump-as-markup.
+  // TODO(esprehn): Is this really true?
 
-  var firstChildHTML = document.firstChild.outerHTML;
-  var secondChildHTML = document.firstChild.nextSibling.outerHTML;
-
-  alert("document.firstChild.outerHTML: " + firstChildHTML + "\n" +
-        "document.firstChild.nextSibling.outerHTML: " + secondChildHTML);
+  alert("document.documentElement.outerHTML: " + document.documentElement.outerHTML + "\n" +
+        "document.childNodes.length: " + document.childNodes.length + "\n" +
+        "b element: " + b + "\n");
 }
 
 window.addEventListener("load", go, false);