Support style invalidation for ::content.

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 2a2c36afcfae59ee734f4ac7a3fc5483ac2a4a99..c181f890e8439afb7a447790931bac0dfe8d55a9 100644
--- a/Source/core/css/CSSSelector.h
+++ b/Source/core/css/CSSSelector.h
@@ -297,7 +297,8 @@ namespace blink {
         bool isContentPseudoElement() const;
         bool isShadowPseudoElement() const;
         bool isHostPseudoClass() const;
-
+        bool isTreeBoundaryCrossing() const;
+        bool isInsertionPointCrossing() const;
         // FIXME: selectors with no tagHistory() get a relation() of Descendant (and sometimes even SubSelector). It should instead be
         // None.
         Relation relation() const { return static_cast<Relation>(m_relation); }
@@ -447,6 +448,17 @@ inline bool CSSSelector::isShadowPseudoElement() const
     return m_match == PseudoElement && pseudoType() == PseudoShadow;
 }
 
+inline bool CSSSelector::isTreeBoundaryCrossing() const
+{
+    return m_match == PseudoClass && (pseudoType() == PseudoHost || pseudoType() == PseudoHostContext);
+}
+
+inline bool CSSSelector::isInsertionPointCrossing() const
+{
+    return (m_match == PseudoClass && pseudoType() == PseudoHostContext)
+        || (m_match == PseudoElement && pseudoType() == PseudoContent);
+}
+
 inline void CSSSelector::setValue(const AtomicString& value)
 {
     ASSERT(m_match != Tag);