[Oilpan]: Make StylePropertySet fully garbage collected.

Source/core/css/resolver/MatchResult.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 25 matching lines @@
 
 MatchedProperties::MatchedProperties()
     : possiblyPaddedMember(0)
 {
 }
 
 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);
     MatchedProperties& newProperties = matchedProperties.last();
     newProperties.properties = const_cast<StylePropertySet*>(properties);
     newProperties.linkMatchType = linkMatchType;
     newProperties.whitelistType = propertyWhitelistType;
     matchedRules.append(rule);
 }
 
 } // namespace WebCore