Move some Element specific code from Node::detach to Element::detach.

Source/core/css/invalidation/StyleInvalidator.cpp

Index: Source/core/css/invalidation/StyleInvalidator.cpp
diff --git a/Source/core/css/invalidation/StyleInvalidator.cpp b/Source/core/css/invalidation/StyleInvalidator.cpp
index b2f94cd339c9464652f827fcda7ce6ef215aef00..ddc28c70b6e8607355a4e9245bac2d1f5bca3d2d 100644
--- a/Source/core/css/invalidation/StyleInvalidator.cpp
+++ b/Source/core/css/invalidation/StyleInvalidator.cpp
@@ -68,10 +68,12 @@ StyleInvalidator::InvalidationList& StyleInvalidator::ensurePendingInvalidationL
     return *addResult.storedValue->value;
 }
 
-void StyleInvalidator::clearInvalidation(Node& node)
+void StyleInvalidator::clearInvalidation(Element& element)
 {
-    if (node.isElementNode() && node.needsStyleInvalidation())
-        m_pendingInvalidationMap.remove(toElement(&node));
+    if (!element.needsStyleInvalidation())
+        return;
+    m_pendingInvalidationMap.remove(&element);
+    element.clearNeedsStyleInvalidation();
 }
 
 void StyleInvalidator::clearPendingInvalidations()