Move CSSOM classes to using MutableStylePropertySet over StylePropertySet.

Source/core/css/StylePropertySet.h

Index: Source/core/css/StylePropertySet.h
diff --git a/Source/core/css/StylePropertySet.h b/Source/core/css/StylePropertySet.h
index d9a4012e417c5101d715dd31ce401f053748c744..e8bc843c1d6c63c7df37e8149299f8b4f21053ab 100644
--- a/Source/core/css/StylePropertySet.h
+++ b/Source/core/css/StylePropertySet.h
@@ -147,8 +147,6 @@ public:
     String asText() const;
 
     PropertySetCSSStyleDeclaration* cssStyleDeclaration();
-    CSSStyleDeclaration* ensureCSSStyleDeclaration();
-    CSSStyleDeclaration* ensureInlineCSSStyleDeclaration(const StyledElement* parentElement);
 
     bool isMutable() const { return m_isMutable; }
     bool hasCSSOMWrapper() const { return m_ownsCSSOMWrapper; }
@@ -228,6 +226,9 @@ public:
 
     MutableStylePropertySet(const StylePropertySet&);
 
+    CSSStyleDeclaration* ensureCSSStyleDeclaration();
+    CSSStyleDeclaration* ensureInlineCSSStyleDeclaration(const StyledElement* parentElement);
+
     Vector<CSSProperty, 4> m_propertyVector;
 
 private: