Move create() methods from StylePropertySet to MutableStylePropertySet.

Source/core/css/FontLoader.cpp

 /*
  * Copyright (C) 2013 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 288 matching lines @@
 }
 
 static void applyPropertyToCurrentStyle(StyleResolver* styleResolver, CSSPropertyID id, const RefPtr<StylePropertySet>& parsedStyle)
 {
     styleResolver->applyPropertyToCurrentStyle(id, parsedStyle->getPropertyCSSValue(id).get());
 }
 
 bool FontLoader::resolveFontStyle(const String& fontString, Font& font)
 {
     // Interpret fontString in the same way as the 'font' attribute of CanvasRenderingContext2D.
-    RefPtr<StylePropertySet> parsedStyle = StylePropertySet::create();
+    RefPtr<MutableStylePropertySet> parsedStyle = MutableStylePropertySet::create();
     CSSParser::parseValue(parsedStyle.get(), CSSPropertyFont, fontString, true, CSSStrictMode, 0);
     if (parsedStyle->isEmpty())
         return false;
 
     String fontValue = parsedStyle->getPropertyValue(CSSPropertyFont);
     if (fontValue == "inherit" || fontValue == "initial")
         return false;
 
     RefPtr<RenderStyle> style = RenderStyle::create();
 
@@ skipping 23 matching lines @@
     applyPropertyToCurrentStyle(styleResolver, CSSPropertyFontSize, parsedStyle);
     styleResolver->updateFont();
     applyPropertyToCurrentStyle(styleResolver, CSSPropertyLineHeight, parsedStyle);
 
     font = style->font();
     font.update(styleResolver->fontSelector());
     return true;
 }
 
 } // namespace WebCore