Use hash set instead of vector for changed RuleSets.

third_party/WebKit/Source/core/dom/StyleEngineTest.cpp

Index: third_party/WebKit/Source/core/dom/StyleEngineTest.cpp
diff --git a/third_party/WebKit/Source/core/dom/StyleEngineTest.cpp b/third_party/WebKit/Source/core/dom/StyleEngineTest.cpp
index fcac598f633f1aace508d038e37520358419e042..0d586c716e5397ebc9dd233b03aa8c21c61c0ff9 100644
--- a/third_party/WebKit/Source/core/dom/StyleEngineTest.cpp
+++ b/third_party/WebKit/Source/core/dom/StyleEngineTest.cpp
@@ -50,13 +50,13 @@ StyleEngineTest::scheduleInvalidationsForRules(TreeScope& treeScope,
   StyleSheetContents* sheet =
       StyleSheetContents::create(CSSParserContext(HTMLStandardMode, nullptr));
   sheet->parseString(cssText);
-  HeapVector<Member<RuleSet>> ruleSets;
+  HeapHashSet<Member<RuleSet>> ruleSets;
   RuleSet& ruleSet = sheet->ensureRuleSet(MediaQueryEvaluator(),
                                           RuleHasDocumentSecurityOrigin);
   ruleSet.compactRulesIfNeeded();
   if (ruleSet.needsFullRecalcForRuleSetInvalidation())
     return RuleSetInvalidationFullRecalc;
-  ruleSets.append(&ruleSet);
+  ruleSets.add(&ruleSet);
   styleEngine().scheduleInvalidationsForRuleSets(treeScope, ruleSets);
   return RuleSetInvalidationsScheduled;
 }