Move create() methods from StylePropertySet to MutableStylePropertySet.

Source/core/editing/Editor.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  * 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 1070 matching lines @@
     Node* focusedNode = frame()->document()->focusedNode();
     if (focusedNode && isHTMLTextFormControlElement(focusedNode)) {
         if (direction == NaturalWritingDirection)
             return;
         toHTMLElement(focusedNode)->setAttribute(dirAttr, direction == LeftToRightWritingDirection ? "ltr" : "rtl");
         focusedNode->dispatchInputEvent();
         frame()->document()->updateStyleIfNeeded();
         return;
     }
 
-    RefPtr<StylePropertySet> style = StylePropertySet::create();
+    RefPtr<MutableStylePropertySet> style = MutableStylePropertySet::create();
     style->setProperty(CSSPropertyDirection, direction == LeftToRightWritingDirection ? "ltr" : direction == RightToLeftWritingDirection ? "rtl" : "inherit", false);
     applyParagraphStyleToSelection(style.get(), EditActionSetWritingDirection);
 }
 
 WritingDirection Editor::baseWritingDirectionForSelectionStart() const
 {
     WritingDirection result = LeftToRightWritingDirection;
 
     Position pos = m_frame->selection()->selection().visibleStart().deepEquivalent();
     Node* node = pos.deprecatedNode();
@@ skipping 1246 matching lines @@
 
     return checkingTypes;
 }
 
 bool Editor::unifiedTextCheckerEnabled() const
 {
     return WebCore::unifiedTextCheckerEnabled(m_frame);
 }
 
 } // namespace WebCore