Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/css/RuleFeature.cpp

Index: Source/core/css/RuleFeature.cpp
diff --git a/Source/core/css/RuleFeature.cpp b/Source/core/css/RuleFeature.cpp
index 800420dff1db91fd3ded89bd6b1f3a5e888b5398..c019ed191dc21fdd036340b9fec0477cc22a0804 100644
--- a/Source/core/css/RuleFeature.cpp
+++ b/Source/core/css/RuleFeature.cpp
@@ -210,7 +210,7 @@ bool RuleFeatureSet::classInvalidationRequiresSubtreeRecalc(const AtomicString&
 
 DescendantInvalidationSet& RuleFeatureSet::ensureClassInvalidationSet(const AtomicString& className)
 {
-    InvalidationSetMap::AddResult addResult = m_classInvalidationSets.add(className, 0);
+    InvalidationSetMap::AddResult addResult = m_classInvalidationSets.add(className, nullptr);
     if (addResult.isNewEntry)
         addResult.storedValue->value = DescendantInvalidationSet::create();
     return *addResult.storedValue->value;