[Oilpan]: Make StylePropertySet fully garbage collected.

Source/core/editing/EditingStyle.cpp

 /*
  * Copyright (C) 2007, 2008, 2009 Apple Computer, Inc.
  * Copyright (C) 2010, 2011 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 1209 matching lines @@
         if (!styleFromMatchedRules->getPropertyCSSValue(CSSPropertyFloat) && getIdentifierValue(m_mutableStyle.get(), CSSPropertyFloat) == CSSValueNone)
             m_mutableStyle->removeProperty(CSSPropertyFloat);
     }
 }
 
 void EditingStyle::removePropertiesInElementDefaultStyle(Element* element)
 {
     if (!m_mutableStyle || m_mutableStyle->isEmpty())
         return;
 
-    RefPtr<StylePropertySet> defaultStyle = styleFromMatchedRulesForElement(element, StyleResolver::UAAndUserCSSRules);
+    RefPtrWillBeRawPtr<StylePropertySet> defaultStyle = styleFromMatchedRulesForElement(element, StyleResolver::UAAndUserCSSRules);
 
     removePropertiesInStyle(m_mutableStyle.get(), defaultStyle.get());
 }
 
 void EditingStyle::forceInline()
 {
     if (!m_mutableStyle)
         m_mutableStyle = MutableStylePropertySet::create();
     const bool propertyIsImportant = true;
     m_mutableStyle->setProperty(CSSPropertyDisplay, CSSValueInline, propertyIsImportant);
@@ skipping 414 matching lines @@
 {
     for (Node* ancestor = node; ancestor; ancestor = ancestor->parentNode()) {
         RefPtrWillBeRawPtr<CSSComputedStyleDeclaration> ancestorStyle = CSSComputedStyleDeclaration::create(ancestor);
         if (!hasTransparentBackgroundColor(ancestorStyle.get()))
             return ancestorStyle->getPropertyCSSValue(CSSPropertyBackgroundColor);
     }
     return nullptr;
 }
 
 }