Move create() methods from StylePropertySet to MutableStylePropertySet.

Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 889 matching lines @@
     return ProcessingInstruction::create(this, target, data);
 }
 
 PassRefPtr<Text> Document::createEditingTextNode(const String& text)
 {
     return Text::createEditingText(this, text);
 }
 
 PassRefPtr<CSSStyleDeclaration> Document::createCSSStyleDeclaration()
 {
-    return StylePropertySet::create()->ensureCSSStyleDeclaration();
+    return MutableStylePropertySet::create()->ensureCSSStyleDeclaration();
 }
 
 PassRefPtr<Node> Document::importNode(Node* importedNode, bool deep, ExceptionCode& ec)
 {
     ec = 0;
 
     if (!importedNode) {
         ec = NOT_SUPPORTED_ERR;
         return 0;
     }
@@ skipping 4700 matching lines @@
         return;
 
     Vector<RefPtr<Element> > associatedFormControls;
     copyToVector(m_associatedFormControls, associatedFormControls);
 
     frame()->page()->chrome()->client()->didAssociateFormControls(associatedFormControls);
     m_associatedFormControls.clear();
 }
 
 } // namespace WebCore