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

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

 // Copyright 2016 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 StyleCalcLength_h
 #define StyleCalcLength_h
 
 #include "core/css/cssom/LengthValue.h"
 #include "wtf/BitVector.h"
 
@@ skipping 26 matching lines @@
     GETTER_MACRO(vmin, LengthUnit::Vmin)
     GETTER_MACRO(vmax, LengthUnit::Vmax)
     GETTER_MACRO(cm, LengthUnit::Cm)
     GETTER_MACRO(mm, LengthUnit::Mm)
     GETTER_MACRO(in, LengthUnit::In)
     GETTER_MACRO(pc, LengthUnit::Pc)
     GETTER_MACRO(pt, LengthUnit::Pt)
 
 #undef GETTER_MACRO
 
-    String cssString() const override;
     PassRefPtrWillBeRawPtr<CSSValue> toCSSValue() const override;
 
     StyleValueType type() const override { return CalcLengthType; }
 protected:
     LengthValue* addInternal(const LengthValue* other, ExceptionState&) override;
     LengthValue* subtractInternal(const LengthValue* other, ExceptionState&) override;
     LengthValue* multiplyInternal(double, ExceptionState&) override;
     LengthValue* divideInternal(double, ExceptionState&) override;
 
 private:
@@ skipping 25 matching lines @@
 #define DEFINE_CALC_LENGTH_TYPE_CASTS(argumentType) \
     DEFINE_TYPE_CASTS(StyleCalcLength, argumentType, value, \
         value->type() == LengthValue::StyleValueType::CalcLengthType, \
         value.type() == LengthValue::StyleValueType::CalcLengthType)
 
 DEFINE_CALC_LENGTH_TYPE_CASTS(StyleValue);
 
 } // namespace blink
 
 #endif