Add assert that updateLayoutTree clears dirty bits.

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index 5de0390a18066f89d4c6313834d575e3c1740414..7f3bc1e10d1da738b1115c80fba26d87a5170fc5 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -1458,6 +1458,13 @@ void Element::attach(const AttachContext& context)
     if (!isActiveInsertionPoint(*this))
         LayoutTreeBuilderForElement(*this, context.resolvedStyle).createLayoutObjectIfNeeded();
 
+    if (hasRareData() && !layoutObject()) {
+        if (ElementAnimations* elementAnimations = elementRareData()->elementAnimations()) {
+            elementAnimations->cssAnimations().cancel();
+            elementAnimations->setAnimationStyleChange(false);
+        }
+    }
+
     addCallbackSelectors();
 
     StyleResolverParentScope parentScope(*this);
@@ -1477,13 +1484,6 @@ void Element::attach(const AttachContext& context)
     // children are attached because the first letter text could come
     // from any of them.
     createPseudoElementIfNeeded(FIRST_LETTER);
-
-    if (hasRareData() && !layoutObject()) {
-        if (ElementAnimations* elementAnimations = elementRareData()->elementAnimations()) {
-            elementAnimations->cssAnimations().cancel();
-            elementAnimations->setAnimationStyleChange(false);
-        }
-    }
 }
 
 void Element::detach(const AttachContext& context)