Remove fallback matching ::cue* pseudo-element selectors

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 56ea79165f6dd005f892ae0bc47b1e899436df51..100241c79d3b8771cb111261745be63fc82dbcef 100644
--- a/Source/core/css/CSSSelector.h
+++ b/Source/core/css/CSSSelector.h
@@ -205,7 +205,6 @@ namespace blink {
             PseudoFullScreenAncestor,
             PseudoInRange,
             PseudoOutOfRange,
-            PseudoUserAgentCustomElement,
             PseudoWebKitCustomElement,
             PseudoCue,
             PseudoFutureCue,
@@ -405,7 +404,7 @@ inline bool CSSSelector::matchesPseudoElement() const
 
 inline bool CSSSelector::isCustomPseudoElement() const
 {
-    return m_match == PseudoElement && (m_pseudoType == PseudoUserAgentCustomElement || m_pseudoType == PseudoWebKitCustomElement);
+    return m_match == PseudoElement && m_pseudoType == PseudoWebKitCustomElement;
 }
 
 inline bool CSSSelector::isHostPseudoClass() const