StyleResolver should update RuleSets lazily.

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index bfe9fa213256414e5236a3573e90fef16f1392a1..252386dacd08b9ddcaa2b146cd2b6076f7ec6b90 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -979,7 +979,7 @@ void Element::attributeChanged(const QualifiedName& name, const AtomicString& ne
         AtomicString newId = makeIdForStyleResolution(newValue, document().inQuirksMode());
         if (newId != oldId) {
             elementData()->setIdForStyleResolution(newId);
-            shouldInvalidateStyle = testShouldInvalidateStyle && checkNeedsStyleInvalidationForIdChange(oldId, newId, styleResolver->ruleFeatureSet());
+            shouldInvalidateStyle = testShouldInvalidateStyle && checkNeedsStyleInvalidationForIdChange(oldId, newId, styleResolver->ensureRuleFeatureSet());
         }
     } else if (name == classAttr) {
         classAttributeChanged(newValue);
@@ -1094,10 +1094,10 @@ void Element::classAttributeChanged(const AtomicString& newClassString)
         const SpaceSplitString oldClasses = elementData()->classNames();
         elementData()->setClass(newClassString, shouldFoldCase);
         const SpaceSplitString& newClasses = elementData()->classNames();
-        shouldInvalidateStyle = testShouldInvalidateStyle && checkSelectorForClassChange(oldClasses, newClasses, styleResolver->ruleFeatureSet());
+        shouldInvalidateStyle = testShouldInvalidateStyle && checkSelectorForClassChange(oldClasses, newClasses, styleResolver->ensureRuleFeatureSet());
     } else {
         const SpaceSplitString& oldClasses = elementData()->classNames();
-        shouldInvalidateStyle = testShouldInvalidateStyle && checkSelectorForClassChange(oldClasses, styleResolver->ruleFeatureSet());
+        shouldInvalidateStyle = testShouldInvalidateStyle && checkSelectorForClassChange(oldClasses, styleResolver->ensureRuleFeatureSet());
         elementData()->clearClass();
     }
 
@@ -2968,7 +2968,7 @@ void Element::updateLabel(TreeScope& scope, const AtomicString& oldForAttributeV
 
 static bool hasSelectorForAttribute(Document* document, const AtomicString& localName)
 {
-    return document->styleResolver() && document->styleResolver()->ruleFeatureSet().hasSelectorForAttribute(localName);
+    return document->styleResolver() && document->styleResolver()->ensureRuleFeatureSet().hasSelectorForAttribute(localName);
 }
 
 void Element::willModifyAttribute(const QualifiedName& name, const AtomicString& oldValue, const AtomicString& newValue)