Move create() methods from StylePropertySet to MutableStylePropertySet.

Source/core/svg/SVGStyledElement.cpp

Index: Source/core/svg/SVGStyledElement.cpp
diff --git a/Source/core/svg/SVGStyledElement.cpp b/Source/core/svg/SVGStyledElement.cpp
index 3e24fad95f4c24d8ae214e9652cb708dcd48f818..a4f783bef1a70dd40c656074659ad181dd6af1b2 100644
--- a/Source/core/svg/SVGStyledElement.cpp
+++ b/Source/core/svg/SVGStyledElement.cpp
@@ -406,7 +406,7 @@ PassRefPtr<CSSValue> SVGStyledElement::getPresentationAttribute(const String& na
     if (!attr)
         return 0;
 
-    RefPtr<StylePropertySet> style = StylePropertySet::create(SVGAttributeMode);
+    RefPtr<MutableStylePropertySet> style = MutableStylePropertySet::create(SVGAttributeMode);
     CSSPropertyID propertyID = SVGStyledElement::cssPropertyIdForSVGAttributeName(attr->name());
     style->setProperty(propertyID, attr->value());
     RefPtr<CSSValue> cssValue = style->getPropertyCSSValue(propertyID);