Support a negation pseudo-class, :not(), in <content select>

Source/core/html/HTMLContentElement.cpp

Index: Source/core/html/HTMLContentElement.cpp
diff --git a/Source/core/html/HTMLContentElement.cpp b/Source/core/html/HTMLContentElement.cpp
index 5f56d5d13b1ef5c6500d1105a94d5791789e9ada..cc6a1aefcc89770d11157868a5627c7d2f17eaf8 100644
--- a/Source/core/html/HTMLContentElement.cpp
+++ b/Source/core/html/HTMLContentElement.cpp
@@ -83,6 +83,11 @@ void HTMLContentElement::parseAttribute(const QualifiedName& name, const AtomicS
     }
 }
 
+static inline bool includesDisallowedPseudoClass(const CSSSelector& selector)
+{
+    return selector.m_match == CSSSelector::PseudoClass && selector.m_pseudoType != CSSSelector::PseudoNot;
+}
+
 bool HTMLContentElement::validateSelect() const
 {
     ASSERT(!m_shouldParseSelect);
@@ -93,15 +98,15 @@ bool HTMLContentElement::validateSelect() const
     if (!m_selectorList.isValid())
         return false;
 
-    bool disallowPseudoClasses = !RuntimeEnabledFeatures::pseudoClassesInMatchingCriteriaInAuthorShadowTreesEnabled() && containingShadowRoot() && containingShadowRoot()->type() == ShadowRoot::AuthorShadowRoot;
+    bool allowAnyPseudoClasses = RuntimeEnabledFeatures::pseudoClassesInMatchingCriteriaInAuthorShadowTreesEnabled() || (containingShadowRoot() && containingShadowRoot()->type() == ShadowRoot::UserAgentShadowRoot);
 
     for (const CSSSelector* selector = m_selectorList.first(); selector; selector = m_selectorList.next(*selector)) {
         if (!selector->isCompound())
             return false;
-        if (!disallowPseudoClasses)
+        if (allowAnyPseudoClasses)
             continue;
         for (const CSSSelector* subSelector = selector; subSelector; subSelector = subSelector->tagHistory()) {
-            if (subSelector->m_match == CSSSelector::PseudoClass)
+            if (includesDisallowedPseudoClass(*subSelector))
                 return false;
         }
     }