Update StyleValue.cssString() to use existing methods instead of rolling our own.

third_party/WebKit/Source/core/css/cssom/StyleValue.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 StyleValue_h
 #define StyleValue_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "core/CoreExport.h"
 #include "core/css/CSSValue.h"
@@ skipping 12 matching lines @@
         KeywordValueType, SimpleLengthType, CalcLengthType, NumberType, TransformValueType
     };
 
     virtual ~StyleValue() { }
 
     virtual StyleValueType type() const = 0;
 
     static StyleValue* create(const CSSValue&);
     static ScriptValue parse(ScriptState*, const String& property, const String& cssText);
 
-    virtual String cssString() const = 0;
     virtual PassRefPtrWillBeRawPtr<CSSValue> toCSSValue() const = 0;
+    virtual String cssString() const
+    {
+        return toCSSValue()->cssText();
+    }
 
     DEFINE_INLINE_VIRTUAL_TRACE() { }
 
 protected:
     StyleValue() {}
 };
 
 } // namespace blink
 
 #endif