Move create() methods from StylePropertySet to MutableStylePropertySet.

Source/core/css/CSSComputedStyleDeclaration.cpp

 /*
  * Copyright (C) 2004 Zack Rusin <zack@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2011 Sencha, Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
@@ skipping 2887 matching lines @@
 
 PassRefPtr<MutableStylePropertySet> CSSComputedStyleDeclaration::copyPropertiesInSet(const Vector<CSSPropertyID>& properties) const
 {
     Vector<CSSProperty, 256> list;
     list.reserveInitialCapacity(properties.size());
     for (unsigned i = 0; i < properties.size(); ++i) {
         RefPtr<CSSValue> value = getPropertyCSSValue(properties[i]);
         if (value)
             list.append(CSSProperty(properties[i], value.release(), false));
     }
-    return static_pointer_cast<MutableStylePropertySet>(StylePropertySet::create(list.data(), list.size()));
+    return MutableStylePropertySet::create(list.data(), list.size());
 }
 
 void CSSComputedStyleDeclaration::reportMemoryUsage(MemoryObjectInfo* memoryObjectInfo) const
 {
     MemoryClassInfo info(memoryObjectInfo, this, WebCoreMemoryTypes::CSS);
     info.addMember(m_node, "node");
 }
 
 CSSRule* CSSComputedStyleDeclaration::parentRule() const
 {
@@ skipping 67 matching lines @@
     static const CSSPropertyID propertiesAfterSlashSeperator[3] = { CSSPropertyBackgroundSize, CSSPropertyBackgroundOrigin, 
                                                                     CSSPropertyBackgroundClip };
 
     RefPtr<CSSValueList> list = CSSValueList::createSlashSeparated();
     list->append(getCSSPropertyValuesForShorthandProperties(StylePropertyShorthand(propertiesBeforeSlashSeperator, WTF_ARRAY_LENGTH(propertiesBeforeSlashSeperator))));
     list->append(getCSSPropertyValuesForShorthandProperties(StylePropertyShorthand(propertiesAfterSlashSeperator, WTF_ARRAY_LENGTH(propertiesAfterSlashSeperator))));
     return list.release();
 }
 
 } // namespace WebCore