optimizing layout performance when only transform3d matrix changed by

Source/core/rendering/style/RenderStyle.cpp

 /*
  * Copyright (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 440 matching lines @@
             return StyleDifferenceLayout;
 
         if (rareNonInheritedData->m_multiCol.get() != other->rareNonInheritedData->m_multiCol.get()
             && *rareNonInheritedData->m_multiCol.get() != *other->rareNonInheritedData->m_multiCol.get())
             return StyleDifferenceLayout;
 
         if (!transformDataEquivalent(other)) {
             // Don't return early here; instead take note of the type of
             // change, and deal with it when looking at compositing.
             changedContextSensitiveProperties |= ContextSensitivePropertyTransform;
+            // if only diff with transform3d parameters changed
+            if (transform().has3DOperation() && other->transform().has3DOperation()) {
+                changedContextSensitiveProperties |= ContextSensitivePropertyTransform3D;
+            }
+
         }
 
         // If the counter directives change, trigger a relayout to re-calculate counter values and rebuild the counter node tree.
         const CounterDirectiveMap* mapA = rareNonInheritedData->m_counterDirectives.get();
         const CounterDirectiveMap* mapB = other->rareNonInheritedData->m_counterDirectives.get();
         if (!(mapA == mapB || (mapA && mapB && *mapA == *mapB)))
             return StyleDifferenceLayout;
 
         // We only need do layout for opacity changes if adding or losing opacity could trigger a change
         // in us being a stacking context.
@@ skipping 1169 matching lines @@
     // right
     radiiSum = radii.topRight().height() + radii.bottomRight().height();
     if (radiiSum > rect.height())
         factor = std::min(rect.height() / radiiSum, factor);
 
     ASSERT(factor <= 1);
     return factor;
 }
 
 } // namespace WebCore