Should not allow style sharing if grandparents matches different rule chain

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 1560 matching lines @@
     }
 
     InspectorInstrumentation::didRecalculateStyleForElement(this);
 
     if (localChange != NoChange && callbackSelectorsDiffer(oldStyle.get(), newStyle.get()))
         updateCallbackSelectors(oldStyle.get(), newStyle.get());
 
     if (RenderObject* renderer = this->renderer()) {
         if (localChange != NoChange || pseudoStyleCacheIsInvalid(oldStyle.get(), newStyle.get()) || (change == Force && renderer->requiresForcedStyleRecalcPropagation()) || shouldNotifyRendererWithIdenticalStyles()) {
             renderer->setAnimatableStyle(newStyle.get());
-        } else if (needsStyleRecalc()) {
+        } else {
             // Although no change occurred, we use the new style so that the cousin style sharing code won't get
             // fooled into believing this style is the same.
+            // FIXME: We may be able to remove this hack, see discussion in
+            // https://codereview.chromium.org/30453002/
             renderer->setStyleInternal(newStyle.get());
         }
     }
 
     // If "rem" units are used anywhere in the document, and if the document element's font size changes, then go ahead and force font updating
     // all the way down the tree. This is simpler than having to maintain a cache of objects (and such font size changes should be rare anyway).
     if (document().styleEngine()->usesRemUnits() && document().documentElement() == this && oldStyle && newStyle && oldStyle->fontSize() != newStyle->fontSize()) {
         // Cached RenderStyles may depend on the re units.
         document().styleResolver()->invalidateMatchedPropertiesCache();
         return Force;
@@ skipping 2037 matching lines @@
     return 0;
 }
 
 Attribute* UniqueElementData::attributeItem(unsigned index)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(index < length());
     return &m_attributeVector.at(index);
 }
 
 } // namespace WebCore