Recalc sibling styles for forward positional rules on mutations only.

Source/core/dom/Element.h

Index: Source/core/dom/Element.h
diff --git a/Source/core/dom/Element.h b/Source/core/dom/Element.h
index ff846f4c018b728ed8ff8fec2111f6438aebabea..b4f878ac868901d5101f23c0ded60bde68bd0faf 100644
--- a/Source/core/dom/Element.h
+++ b/Source/core/dom/Element.h
@@ -334,6 +334,7 @@ public:
     bool childrenAffectedByFirstChildRules() const { return hasRareData() && rareDataChildrenAffectedByFirstChildRules(); }
     bool childrenAffectedByLastChildRules() const { return hasRareData() && rareDataChildrenAffectedByLastChildRules(); }
     bool childrenAffectedByDirectAdjacentRules() const { return hasRareData() && rareDataChildrenAffectedByDirectAdjacentRules(); }
+    bool childrenAffectedByIndirectAdjacentRules() const { return hasRareData() && rareDataChildrenAffectedByIndirectAdjacentRules(); }
     bool childrenAffectedByForwardPositionalRules() const { return hasRareData() && rareDataChildrenAffectedByForwardPositionalRules(); }
     bool childrenAffectedByBackwardPositionalRules() const { return hasRareData() && rareDataChildrenAffectedByBackwardPositionalRules(); }
     unsigned childIndex() const { return hasRareData() ? rareDataChildIndex() : 0; }
@@ -348,6 +349,7 @@ public:
     void setChildrenAffectedByFirstChildRules();
     void setChildrenAffectedByLastChildRules();
     void setChildrenAffectedByDirectAdjacentRules();
+    void setChildrenAffectedByIndirectAdjacentRules();
     void setChildrenAffectedByForwardPositionalRules();
     void setChildrenAffectedByBackwardPositionalRules();
     void setChildIndex(unsigned);
@@ -643,6 +645,7 @@ private:
     bool rareDataChildrenAffectedByFirstChildRules() const;
     bool rareDataChildrenAffectedByLastChildRules() const;
     bool rareDataChildrenAffectedByDirectAdjacentRules() const;
+    bool rareDataChildrenAffectedByIndirectAdjacentRules() const;
     bool rareDataChildrenAffectedByForwardPositionalRules() const;
     bool rareDataChildrenAffectedByBackwardPositionalRules() const;
     unsigned rareDataChildIndex() const;