StylePropertySerializer should expand all property if needed.

Source/core/css/CSSValueList.h

Index: Source/core/css/CSSValueList.h
diff --git a/Source/core/css/CSSValueList.h b/Source/core/css/CSSValueList.h
index e32f2dc7ba4348b487916261f19abe89789008ce..f66319a87e44c157e0c1e11c3b3f2c11ac391d4b 100644
--- a/Source/core/css/CSSValueList.h
+++ b/Source/core/css/CSSValueList.h
@@ -46,6 +46,7 @@ public:
     CSSValue* item(size_t index) { return m_values[index].get(); }
     const CSSValue* item(size_t index) const { return m_values[index].get(); }
     CSSValue* itemWithBoundsCheck(size_t index) { return index < m_values.size() ? m_values[index].get() : 0; }
+    const CSSValue* itemWithBoundsCheck(size_t index) const { return index < m_values.size() ? m_values[index].get() : 0; }
 
     void append(PassRefPtrWillBeRawPtr<CSSValue> value) { m_values.append(value); }
     void prepend(PassRefPtrWillBeRawPtr<CSSValue> value) { m_values.prepend(value); }