Implement ::placeholder CSS selector.

third_party/WebKit/Source/core/css/parser/CSSParserSelector.h

 /*
  * Copyright (C) 2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2008, 2009, 2010 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.
  *
@@ skipping 80 matching lines @@
     return m_selector->getPseudoType();
   }
   const CSSSelectorList* selectorList() const {
     return m_selector->selectorList();
   }
 
   bool needsImplicitShadowCombinatorForMatching() const {
     return pseudoType() == CSSSelector::PseudoWebKitCustomElement ||
            pseudoType() == CSSSelector::PseudoBlinkInternalElement ||
            pseudoType() == CSSSelector::PseudoCue ||
+           pseudoType() == CSSSelector::PseudoPlaceholder ||
            pseudoType() == CSSSelector::PseudoShadow ||
            pseudoType() == CSSSelector::PseudoSlotted;
   }
 
   bool isSimple() const;
 
   CSSParserSelector* tagHistory() const { return m_tagHistory.get(); }
   void setTagHistory(std::unique_ptr<CSSParserSelector> selector) {
     m_tagHistory = std::move(selector);
   }
   void clearTagHistory() { m_tagHistory.reset(); }
   void appendTagHistory(CSSSelector::RelationType,
                         std::unique_ptr<CSSParserSelector>);
   std::unique_ptr<CSSParserSelector> releaseTagHistory();
   void prependTagSelector(const QualifiedName&, bool tagIsImplicit = false);
 
  private:
   std::unique_ptr<CSSSelector> m_selector;
   std::unique_ptr<CSSParserSelector> m_tagHistory;
 };
 
 }  // namespace blink
 
 #endif