[Typed OM] Add an "UnsupportedStyleValue" in C++ that just has a string for unknown types

third_party/WebKit/Source/core/css/cssom/CSSStyleValue.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CSSStyleValue_h
 #define CSSStyleValue_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
+#include "core/CSSPropertyNames.h"
 #include "core/CoreExport.h"
 #include "core/css/CSSValue.h"
 
 namespace blink {
 
 class ExceptionState;
 class ScriptState;
 class ScriptValue;
 
 class CORE_EXPORT CSSStyleValue : public GarbageCollectedFinalized<CSSStyleValue>, public ScriptWrappable {
     WTF_MAKE_NONCOPYABLE(CSSStyleValue);
     DEFINE_WRAPPERTYPEINFO();
 public:
     enum StyleValueType {
+        Unknown,
         AngleType,
         CalcLengthType,
         KeywordType,
         NumberType,
         PositionType,
         SimpleLengthType,
         TransformType,
     };
 
     virtual ~CSSStyleValue() { }
 
     virtual StyleValueType type() const = 0;
 
     static ScriptValue parse(ScriptState*, const String& propertyName, const String& value, ExceptionState&);
 
     virtual CSSValue* toCSSValue() const = 0;
+    virtual CSSValue* toCSSValueWithProperty(CSSPropertyID) const
+    {
+        return toCSSValue();
+    }
     virtual String cssString() const
     {
         return toCSSValue()->cssText();
     }
 
     DEFINE_INLINE_VIRTUAL_TRACE() { }
 
 protected:
     CSSStyleValue() {}
 };
 
 typedef HeapVector<Member<CSSStyleValue>> CSSStyleValueVector;
 
 } // namespace blink
 
 #endif