[Oilpan]: Make StylePropertySet fully garbage collected.

Source/core/css/resolver/MatchResult.cpp

Index: Source/core/css/resolver/MatchResult.cpp
diff --git a/Source/core/css/resolver/MatchResult.cpp b/Source/core/css/resolver/MatchResult.cpp
index 1419f5931dcbc242e034840fad356c33e813a3ac..bfef7c6b07a741e8100b98a8faafa03fda4e77d3 100644
--- a/Source/core/css/resolver/MatchResult.cpp
+++ b/Source/core/css/resolver/MatchResult.cpp
@@ -43,6 +43,11 @@ MatchedProperties::~MatchedProperties()
 {
 }
 
+void MatchedProperties::trace(Visitor* visitor)
+{
+    visitor->trace(properties);
+}
+
 void MatchResult::addMatchedProperties(const StylePropertySet* properties, StyleRule* rule, unsigned linkMatchType, PropertyWhitelistType propertyWhitelistType)
 {
     matchedProperties.grow(matchedProperties.size() + 1);