[Oilpan]: Make StylePropertySet fully garbage collected.

Source/core/dom/CSSSelectorWatch.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 126 matching lines @@
     }
     return true;
 }
 
 void CSSSelectorWatch::watchCSSSelectors(const Vector<String>& selectors)
 {
     m_watchedCallbackSelectors.clear();
     BisonCSSParser parser(CSSParserContext(UASheetMode, 0));
 
     const CSSProperty callbackProperty(CSSPropertyInternalCallback, CSSPrimitiveValue::createIdentifier(CSSValueInternalPresence));
-    const RefPtr<StylePropertySet> callbackPropertySet = ImmutableStylePropertySet::create(&callbackProperty, 1, UASheetMode);
+    const RefPtrWillBeRawPtr<StylePropertySet> callbackPropertySet = ImmutableStylePropertySet::create(&callbackProperty, 1, UASheetMode);
 
     CSSSelectorList selectorList;
     for (unsigned i = 0; i < selectors.size(); ++i) {
         parser.parseSelector(selectors[i], selectorList);
         if (!selectorList.isValid())
             continue;
 
         // Only accept Compound Selectors, since they're cheaper to match.
         if (!allCompound(selectorList))
             continue;
 
         RefPtrWillBeRawPtr<StyleRule> rule = StyleRule::create();
         rule->wrapperAdoptSelectorList(selectorList);
         rule->setProperties(callbackPropertySet);
         m_watchedCallbackSelectors.append(rule.release());
     }
     m_document.changedSelectorWatch();
 }
 
 void CSSSelectorWatch::trace(Visitor* visitor)
 {
     visitor->trace(m_watchedCallbackSelectors);
     DocumentSupplement::trace(visitor);
 }
 
 } // namespace WebCore