Make a '::distributed' pseudo element the first-ever client who can accept a relative selector.

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 2ec1ec9a5ad99f4bc5d8b1de0fc82ec39a75bef6..e8fc3ae32fc224b7a45151f6d2f39f4816c5fe53 100644
--- a/Source/core/css/CSSSelector.h
+++ b/Source/core/css/CSSSelector.h
@@ -79,8 +79,7 @@ namespace WebCore {
             DirectAdjacent,
             IndirectAdjacent,
             SubSelector,
-            ShadowPseudo,
-            ShadowDistributed
+            ShadowPseudo
         };
 
         enum PseudoType {
@@ -220,7 +219,6 @@ namespace WebCore {
         bool isSiblingSelector() const;
         bool isAttributeSelector() const;
         bool isDistributedPseudoElement() const;
-        bool isShadowDistributed() const;
 
         Relation relation() const { return static_cast<Relation>(m_relation); }
 
@@ -234,6 +232,9 @@ namespace WebCore {
         bool isForPage() const { return m_isForPage; }
         void setForPage() { m_isForPage = true; }
 
+        bool relationIsForShadowDistributed() const { return m_relationIsForShadowDistributed; }
+        void setRelationIsForShadowDistributed() { m_relationIsForShadowDistributed = true; }
+
         unsigned m_relation           : 3; // enum Relation
         mutable unsigned m_match      : 4; // enum Match
         mutable unsigned m_pseudoType : 8; // PseudoType
@@ -245,6 +246,7 @@ namespace WebCore {
         unsigned m_hasRareData            : 1;
         unsigned m_isForPage              : 1;
         unsigned m_tagIsForNamespaceRule  : 1;
+        unsigned m_relationIsForShadowDistributed  : 1;
 
         unsigned specificityForOneSelector() const;
         unsigned specificityForPage() const;
@@ -338,11 +340,6 @@ inline bool CSSSelector::isDistributedPseudoElement() const
     return m_match == PseudoElement && pseudoType() == PseudoDistributed;
 }
 
-inline bool CSSSelector::isShadowDistributed() const
-{
-    return m_relation == CSSSelector::ShadowDistributed;
-}
-
 inline void CSSSelector::setValue(const AtomicString& value)
 {
     ASSERT(m_match != Tag);
@@ -371,6 +368,7 @@ inline CSSSelector::CSSSelector()
     , m_hasRareData(false)
     , m_isForPage(false)
     , m_tagIsForNamespaceRule(false)
+    , m_relationIsForShadowDistributed(false)
 {
 }
 
@@ -384,6 +382,7 @@ inline CSSSelector::CSSSelector(const QualifiedName& tagQName, bool tagIsForName
     , m_hasRareData(false)
     , m_isForPage(false)
     , m_tagIsForNamespaceRule(tagIsForNamespaceRule)
+    , m_relationIsForShadowDistributed(false)
 {
     m_data.m_tagQName = tagQName.impl();
     m_data.m_tagQName->ref();
@@ -399,6 +398,7 @@ inline CSSSelector::CSSSelector(const CSSSelector& o)
     , m_hasRareData(o.m_hasRareData)
     , m_isForPage(o.m_isForPage)
     , m_tagIsForNamespaceRule(o.m_tagIsForNamespaceRule)
+    , m_relationIsForShadowDistributed(o.m_relationIsForShadowDistributed)
 {
     if (o.m_match == Tag) {
         m_data.m_tagQName = o.m_data.m_tagQName;