Use hash set instead of vector for changed RuleSets.

third_party/WebKit/Source/core/dom/StyleEngine.h

Index: third_party/WebKit/Source/core/dom/StyleEngine.h
diff --git a/third_party/WebKit/Source/core/dom/StyleEngine.h b/third_party/WebKit/Source/core/dom/StyleEngine.h
index bd4e74ba33d1b2f31aac1b9de642b15d0dc72390..390bcd80d796a59be07eb0213f50175944fca19c 100644
--- a/third_party/WebKit/Source/core/dom/StyleEngine.h
+++ b/third_party/WebKit/Source/core/dom/StyleEngine.h
@@ -250,7 +250,7 @@ class CORE_EXPORT StyleEngine final
                                               Element& afterElement);
   void scheduleNthPseudoInvalidations(ContainerNode&);
   void scheduleInvalidationsForRuleSets(TreeScope&,
-                                        const HeapVector<Member<RuleSet>>&);
+                                        const HeapHashSet<Member<RuleSet>>&);
 
   unsigned styleForElementCount() const { return m_styleForElementCount; }
   void incStyleForElementCount() { m_styleForElementCount++; }
@@ -323,7 +323,7 @@ class CORE_EXPORT StyleEngine final
   bool shouldSkipInvalidationFor(const Element&) const;
   void scheduleRuleSetInvalidationsForElement(
       Element&,
-      const HeapVector<Member<RuleSet>>&);
+      const HeapHashSet<Member<RuleSet>>&);
   void invalidateSlottedElements(HTMLSlotElement&);
 
   void updateViewport();