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

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 569 matching lines @@
         if (current->pseudoType() == CSSSelector::PseudoWindowInactive)
             metadata.usesWindowInactiveSelector = true;
         if (current->relation() == CSSSelector::DirectAdjacent) {
             maxDirectAdjacentSelectors++;
         } else if (maxDirectAdjacentSelectors
             && ((current->relation() != CSSSelector::SubSelector) || current->isLastInTagHistory())) {
             if (maxDirectAdjacentSelectors > metadata.maxDirectAdjacentSelectors)
                 metadata.maxDirectAdjacentSelectors = maxDirectAdjacentSelectors;
             maxDirectAdjacentSelectors = 0;
         }
-        if (current->isSiblingSelector())
+        if (!metadata.foundInsertionPointCrossing && current->isSiblingSelector())
             metadata.foundSiblingSelector = true;
 
-        const CSSSelectorList* selectorList = current->selectorList();
-        if (!selectorList)
-            continue;
-
-        for (const CSSSelector* subSelector = selectorList->first(); subSelector; subSelector = CSSSelectorList::next(*subSelector))
-            collectFeaturesFromSelector(*subSelector, metadata);
+        if (const CSSSelectorList* selectorList = current->selectorList()) {
+            for (const CSSSelector* subSelector = selectorList->first(); subSelector; subSelector = CSSSelectorList::next(*subSelector))
+                collectFeaturesFromSelector(*subSelector, metadata);
+        }
+        if (current->relationIsAffectedByPseudoContent())
+            metadata.foundInsertionPointCrossing = true;
     }
 
     ASSERT(!maxDirectAdjacentSelectors);
 }
 
 void RuleFeatureSet::FeatureMetadata::add(const FeatureMetadata& other)
 {
     usesFirstLineRules = usesFirstLineRules || other.usesFirstLineRules;
     usesWindowInactiveSelector = usesWindowInactiveSelector || other.usesWindowInactiveSelector;
     maxDirectAdjacentSelectors = std::max(maxDirectAdjacentSelectors, other.maxDirectAdjacentSelectors);
 }
 
 void RuleFeatureSet::FeatureMetadata::clear()
 {
     usesFirstLineRules = false;
     usesWindowInactiveSelector = false;
     foundSiblingSelector = false;
+    foundInsertionPointCrossing = false;
     maxDirectAdjacentSelectors = 0;
 }
 
 void RuleFeatureSet::add(const RuleFeatureSet& other)
 {
     for (const auto& entry : other.m_classInvalidationSets)
         ensureInvalidationSet(m_classInvalidationSets, entry.key, entry.value->type()).combine(*entry.value);
     for (const auto& entry : other.m_attributeInvalidationSets)
         ensureInvalidationSet(m_attributeInvalidationSets, entry.key, entry.value->type()).combine(*entry.value);
     for (const auto& entry : other.m_idInvalidationSets)
@@ skipping 104 matching lines @@
 
 DEFINE_TRACE(RuleFeatureSet)
 {
 #if ENABLE(OILPAN)
     visitor->trace(siblingRules);
     visitor->trace(uncommonAttributeRules);
 #endif
 }
 
 } // namespace blink