Custom pseudo element types as an invalidation set feature.

Source/core/css/invalidation/StyleInvalidator.cpp

Index: Source/core/css/invalidation/StyleInvalidator.cpp
diff --git a/Source/core/css/invalidation/StyleInvalidator.cpp b/Source/core/css/invalidation/StyleInvalidator.cpp
index fe400494f515777168ffb5def3c8e6dbd9129aff..00a82dc7d8ce873117cf0181c1e7a60a7ede05bc 100644
--- a/Source/core/css/invalidation/StyleInvalidator.cpp
+++ b/Source/core/css/invalidation/StyleInvalidator.cpp
@@ -34,6 +34,7 @@ void StyleInvalidator::RecursionData::pushInvalidationSet(const DescendantInvali
 {
     invalidationSet.getClasses(m_invalidationClasses);
     invalidationSet.getAttributes(m_invalidationAttributes);
+    m_invalidateCustomPseudo = invalidationSet.customPseudoInvalid();
     m_foundInvalidationSet = true;
 }
 
@@ -52,6 +53,8 @@ bool StyleInvalidator::RecursionData::matchesCurrentInvalidationSets(Element& el
                 return true;
         }
     }
+    if (m_invalidateCustomPseudo && element.shadowPseudoId() != nullAtom)
+        return true;
 
     return false;
 }