Recalc sibling styles for forward positional rules on mutations only.

Source/core/dom/shadow/ShadowRoot.h

Index: Source/core/dom/shadow/ShadowRoot.h
diff --git a/Source/core/dom/shadow/ShadowRoot.h b/Source/core/dom/shadow/ShadowRoot.h
index 43091ff3ecb6104f1b1fb75ee70067a3814547f5..4905c5fbeb79990a5700e66150f61d6b8cae1b58 100644
--- a/Source/core/dom/shadow/ShadowRoot.h
+++ b/Source/core/dom/shadow/ShadowRoot.h
@@ -132,12 +132,14 @@ public:
     bool childrenAffectedByFirstChildRules() const;
     bool childrenAffectedByLastChildRules() const;
     bool childrenAffectedByDirectAdjacentRules() const;
+    bool childrenAffectedByIndirectAdjacentRules() const;
     bool childrenAffectedByForwardPositionalRules() const;
     bool childrenAffectedByBackwardPositionalRules() const;
 
     void setChildrenAffectedByFirstChildRules();
     void setChildrenAffectedByLastChildRules();
     void setChildrenAffectedByDirectAdjacentRules();
+    void setChildrenAffectedByIndirectAdjacentRules();
     void setChildrenAffectedByForwardPositionalRules();
     void setChildrenAffectedByBackwardPositionalRules();