Element::recalcStyle() overly reattach()-es InsertionPoints.

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 f1676dd89408cfae9f6ce1eac58c1c09663cecd6..33c8cd5b322f0294c6b00618de2b8af9394e11de 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -1388,7 +1388,12 @@ void Element::recalcStyle(StyleChange change)
             // common, especially during lazy attach.
             newStyle = styleForRenderer();
             localChange = Node::diff(currentStyle.get(), newStyle.get(), document());
+        } else if (isActiveInsertionPoint(this) && attached()) {
+            // Active Insertion points are special: They never have renderers and reattach()-ing their subtrees is just a waste.
+            // We can just skip Element-local style updates for them.
+            localChange = change;
         }
+
         if (localChange == Detach) {
             // FIXME: The style gets computed twice by calling attach. We could do better if we passed the style along.
             reattach();