Don't add siblingRules with combinator left of ::content.

third_party/WebKit/Source/core/css/RuleFeature.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 90 matching lines @@
     InvalidationSet* invalidationSetForSelector(const CSSSelector&, InvalidationType);
 
 private:
     // Each map entry is either a DescendantInvalidationSet or SiblingInvalidationSet.
     // When both are needed, we store the SiblingInvalidationSet, and use it to hold the DescendantInvalidationSet.
     using InvalidationSetMap = HashMap<AtomicString, RefPtr<InvalidationSet>>;
     using PseudoTypeInvalidationSetMap = HashMap<CSSSelector::PseudoType, RefPtr<InvalidationSet>, WTF::IntHash<unsigned>, WTF::UnsignedWithZeroKeyHashTraits<unsigned>>;
 
     struct FeatureMetadata {
         DISALLOW_NEW();
-        FeatureMetadata()
-            : usesFirstLineRules(false)
-            , usesWindowInactiveSelector(false)
-            , foundSiblingSelector(false)
-            , maxDirectAdjacentSelectors(0)
-        { }
         void add(const FeatureMetadata& other);
         void clear();
 
-        bool usesFirstLineRules;
-        bool usesWindowInactiveSelector;
-        bool foundSiblingSelector;
-        unsigned maxDirectAdjacentSelectors;
+        bool usesFirstLineRules = false;
+        bool usesWindowInactiveSelector = false;
+        bool foundSiblingSelector = false;
+        bool foundInsertionPointCrossing = false;
+        unsigned maxDirectAdjacentSelectors = 0;
     };
 
     void collectFeaturesFromSelector(const CSSSelector&, FeatureMetadata&);
 
     InvalidationSet& ensureClassInvalidationSet(const AtomicString& className, InvalidationType);
     InvalidationSet& ensureAttributeInvalidationSet(const AtomicString& attributeName, InvalidationType);
     InvalidationSet& ensureIdInvalidationSet(const AtomicString& id, InvalidationType);
     InvalidationSet& ensurePseudoInvalidationSet(CSSSelector::PseudoType, InvalidationType);
 
     void updateInvalidationSets(const RuleData&);
@@ skipping 35 matching lines @@
     PseudoTypeInvalidationSetMap m_pseudoInvalidationSets;
 
     friend class RuleFeatureSetTest;
 };
 
 } // namespace blink
 
 WTF_ALLOW_MOVE_AND_INIT_WITH_MEM_FUNCTIONS(blink::RuleFeature);
 
 #endif // RuleFeature_h