Consistently use on-heap collections for StyleRuleBase descendants.

Source/core/css/resolver/MatchResult.h

Index: Source/core/css/resolver/MatchResult.h
diff --git a/Source/core/css/resolver/MatchResult.h b/Source/core/css/resolver/MatchResult.h
index bbcae30bdb5ea9293a6b1aa2d712591fff44cb33..25d9b91900a50be0e24b2af3e7725e6e291714ea 100644
--- a/Source/core/css/resolver/MatchResult.h
+++ b/Source/core/css/resolver/MatchResult.h
@@ -67,10 +67,12 @@ struct MatchedProperties {
     };
 };
 
-struct MatchResult {
+class MatchResult {
+    STACK_ALLOCATED();
+public:
     MatchResult() : isCacheable(true) { }
     Vector<MatchedProperties, 64> matchedProperties;
-    Vector<StyleRule*, 64> matchedRules;
+    WillBeHeapVector<RawPtrWillBeMember<StyleRule>, 64> matchedRules;
     MatchRanges ranges;
     bool isCacheable;