Separate method for adding features to an invalidation set.

Source/core/css/RuleFeature.h

Index: Source/core/css/RuleFeature.h
diff --git a/Source/core/css/RuleFeature.h b/Source/core/css/RuleFeature.h
index e28a508152ed77e55fd615667b224d4ee68c97f8..e5bdb0056250dcbec7886142efabdae73c67a139 100644
--- a/Source/core/css/RuleFeature.h
+++ b/Source/core/css/RuleFeature.h
@@ -160,6 +160,8 @@ private:
 
     static void extractInvalidationSetFeature(const CSSSelector&, InvalidationSetFeatures&);
     const CSSSelector* extractInvalidationSetFeatures(const CSSSelector&, InvalidationSetFeatures&, bool negated);
+
+    void addFeaturesToInvalidationSet(DescendantInvalidationSet&, const InvalidationSetFeatures&);
     void addFeaturesToInvalidationSets(const CSSSelector&, InvalidationSetFeatures&);
 
     void addClassToInvalidationSet(const AtomicString& className, Element&);