Move create() methods from StylePropertySet to MutableStylePropertySet.

Source/core/page/DragController.cpp

 /*
  * Copyright (C) 2007, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Google Inc.
  *
  * 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 12 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
  */
 
 #include "config.h"
 #include "core/page/DragController.h"
 
 #include <wtf/CurrentTime.h>
 #include <wtf/RefPtr.h>
 #include "HTMLNames.h"
-#include "core/css/StylePropertySet.h"
 #include "core/dom/Clipboard.h"
 #include "core/dom/ClipboardAccessPolicy.h"
 #include "core/dom/Document.h"
 #include "core/dom/DocumentFragment.h"
 #include "core/dom/Element.h"
 #include "core/dom/ExceptionCodePlaceholder.h"
 #include "core/dom/Node.h"
 #include "core/dom/Text.h"
 #include "core/dom/TextEvent.h"
 #include "core/dom/shadow/ShadowRoot.h"
@@ skipping 875 matching lines @@
 #endif
     return maxDragImageSize;
 }
 
 void DragController::cleanupAfterSystemDrag()
 {
 }
 
 } // namespace WebCore