Use hash set instead of vector for changed RuleSets.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
@@ skipping 232 matching lines @@
   void scheduleSiblingInvalidationsForElement(Element&,
                                               ContainerNode& schedulingParent,
                                               unsigned minDirectAdjacent);
   void scheduleInvalidationsForInsertedSibling(Element* beforeElement,
                                                Element& insertedElement);
   void scheduleInvalidationsForRemovedSibling(Element* beforeElement,
                                               Element& removedElement,
                                               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++; }
 
   StyleResolverStats* stats() { return m_styleResolverStats.get(); }
   void setStatsEnabled(bool);
 
   PassRefPtr<ComputedStyle> findSharedStyle(const ElementResolveContext&);
 
   void applyRuleSetChanges(TreeScope&,
@@ skipping 52 matching lines @@
   }
 
   void updateActiveStyleSheetsInShadow(
       StyleResolverUpdateMode,
       TreeScope*,
       UnorderedTreeScopeSet& treeScopesRemoved);
 
   bool shouldSkipInvalidationFor(const Element&) const;
   void scheduleRuleSetInvalidationsForElement(
       Element&,
-      const HeapVector<Member<RuleSet>>&);
+      const HeapHashSet<Member<RuleSet>>&);
   void invalidateSlottedElements(HTMLSlotElement&);
 
   void updateViewport();
   void updateActiveStyleSheets();
   const MediaQueryEvaluator& ensureMediaQueryEvaluator();
 
   Member<Document> m_document;
   bool m_isMaster;
 
   // Track the number of currently loading top-level stylesheets needed for
@@ skipping 43 matching lines @@
 
   std::unique_ptr<StyleResolverStats> m_styleResolverStats;
   unsigned m_styleForElementCount = 0;
 
   friend class StyleEngineTest;
 };
 
 }  // namespace blink
 
 #endif