Don't add to uncommonAttributeRules for non-sharable cases.

third_party/WebKit/Source/core/css/RuleSet.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 60 matching lines @@
 
 static bool containsUncommonAttributeSelector(const CSSSelector& selector)
 {
     const CSSSelector* current = &selector;
     for (; current; current = current->tagHistory()) {
         // Allow certain common attributes (used in the default style) in the selectors that match the current element.
         if (current->isAttributeSelector() && !isCommonAttributeSelectorAttribute(current->attribute()))
             return true;
         if (selectorListContainsUncommonAttributeSelector(current))
             return true;
+        if (current->relationIsAffectedByPseudoContent()
+            || current->pseudoType() == CSSSelector::PseudoHost
+            || current->pseudoType() == CSSSelector::PseudoHostContext
+            || current->pseudoType() == CSSSelector::PseudoSlotted) {
+            return false;
+        }
         if (current->relation() != CSSSelector::SubSelector) {
             current = current->tagHistory();
             break;
         }
     }
 
     for (; current; current = current->tagHistory()) {
         if (current->isAttributeSelector())
             return true;
         if (selectorListContainsUncommonAttributeSelector(current))
@@ skipping 307 matching lines @@
 
 #ifndef NDEBUG
 void RuleSet::show() const
 {
     for (const auto& rule: m_allRules)
         rule.selector().show();
 }
 #endif
 
 } // namespace blink