Custom pseudo element types as an invalidation set feature.

Source/core/css/RuleFeature.h

Index: Source/core/css/RuleFeature.h
diff --git a/Source/core/css/RuleFeature.h b/Source/core/css/RuleFeature.h
index 2e6a9b74842a82ea439df605d6fbc39ba6ed8ec9..331da05a1601cb1b0870ea6f65782ffa1d38b68c 100644
--- a/Source/core/css/RuleFeature.h
+++ b/Source/core/css/RuleFeature.h
@@ -146,10 +146,12 @@ private:
     InvalidationSetMode updateInvalidationSets(const CSSSelector&);
 
     struct InvalidationSetFeatures {
+        InvalidationSetFeatures() : customPseudoElement(false) { }
         Vector<AtomicString> classes;
         Vector<AtomicString> attributes;
         AtomicString id;
         AtomicString tagName;
+        bool customPseudoElement;
     };
 
     static void extractInvalidationSetFeature(const CSSSelector&, InvalidationSetFeatures&);