Move create() methods from StylePropertySet to MutableStylePropertySet.

Source/core/html/canvas/CanvasRenderingContext2D.cpp

Index: Source/core/html/canvas/CanvasRenderingContext2D.cpp
diff --git a/Source/core/html/canvas/CanvasRenderingContext2D.cpp b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
index 72e701e3063e77aacdf3c4134c67dc1a670b9ebc..14a57200401d8f49ef197d41b25548874d325ea6 100644
--- a/Source/core/html/canvas/CanvasRenderingContext2D.cpp
+++ b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
@@ -1975,7 +1975,7 @@ void CanvasRenderingContext2D::setFont(const String& newFont)
     if (newFont == state().m_unparsedFont && state().m_realizedFont)
         return;
 
-    RefPtr<StylePropertySet> parsedStyle = StylePropertySet::create();
+    RefPtr<MutableStylePropertySet> parsedStyle = MutableStylePropertySet::create();
     CSSParser::parseValue(parsedStyle.get(), CSSPropertyFont, newFont, true, strictToCSSParserMode(!m_usesCSSCompatibilityParseMode), 0);
     if (parsedStyle->isEmpty())
         return;