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

Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 1370 matching lines @@
     }
     if (hasParentStyle && (change >= Inherit || needsStyleRecalc())) {
         StyleChange localChange = Detach;
         RefPtr<RenderStyle> newStyle;
         if (currentStyle) {
             // FIXME: This still recalcs style twice when changing display types, but saves
             // us from recalcing twice when going from none -> anything else which is more
             // 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();
             // attach recalculates the style for all children. No need to do it twice.
             clearNeedsStyleRecalc();
             clearChildNeedsStyleRecalc();
 
             if (hasCustomStyleCallbacks())
                 didRecalcStyle(change);
             return;
@@ skipping 1702 matching lines @@
     return 0;
 }
 
 Attribute* UniqueElementData::attributeItem(unsigned index)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(index < length());
     return &m_attributeVector.at(index);
 }
 
 } // namespace WebCore