Remove ::part.

Source/core/css/CSSSelector.h

Index: Source/core/css/CSSSelector.h
diff --git a/Source/core/css/CSSSelector.h b/Source/core/css/CSSSelector.h
index 889726188b616f38d4da50bf42f26ea655cbb4b7..0bba6f3e9fa424b51ec2d4351d294a771b9f1eb3 100644
--- a/Source/core/css/CSSSelector.h
+++ b/Source/core/css/CSSSelector.h
@@ -163,7 +163,6 @@ namespace WebCore {
             PseudoPastCue,
             PseudoSeamlessDocument,
             PseudoDistributed,
-            PseudoPart,
             PseudoUnresolved,
             PseudoContent,
             PseudoHost
@@ -207,7 +206,6 @@ namespace WebCore {
         const QualifiedName& attribute() const;
         const AtomicString& argument() const { return m_hasRareData ? m_data.m_rareData->m_argument : nullAtom; }
         const CSSSelectorList* selectorList() const { return m_hasRareData ? m_data.m_rareData->m_selectorList.get() : 0; }
-        bool isMatchUserAgentOnly() const { return m_hasRareData ? m_data.m_rareData->m_matchUserAgentOnly : false; }
 
         void setValue(const AtomicString&);
         void setAttribute(const QualifiedName&);
@@ -275,9 +273,8 @@ namespace WebCore {
             int m_a; // Used for :nth-*
             int m_b; // Used for :nth-*
             QualifiedName m_attribute; // used for attribute selector
-            AtomicString m_argument; // Used for :contains, :lang, :nth-* and ::part
+            AtomicString m_argument; // Used for :contains, :lang, :nth-*
             OwnPtr<CSSSelectorList> m_selectorList; // Used for :-webkit-any and :not
-            unsigned m_matchUserAgentOnly : 1; // Used to make ::part with "-webkit"-prefixed part name match only elements in UA shadow roots.
 
         private:
             RareData(PassRefPtr<StringImpl> value);
@@ -313,7 +310,7 @@ inline bool CSSSelector::isUnknownPseudoElement() const
 
 inline bool CSSSelector::isCustomPseudoElement() const
 {
-    return m_match == PseudoElement && (m_pseudoType == PseudoUserAgentCustomElement || m_pseudoType == PseudoWebKitCustomElement || m_pseudoType == PseudoPart);
+    return m_match == PseudoElement && (m_pseudoType == PseudoUserAgentCustomElement || m_pseudoType == PseudoWebKitCustomElement);
 }
 
 inline bool CSSSelector::isHostPseudoClass() const