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 f06a9b6859179c198baf53422c98ad091bbb39fa..31d5155fe5e2d1daaee556e8fc492800519d1ef5 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -991,7 +991,7 @@ 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);
@@ -1099,10 +1099,10 @@ 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();
     }