Rewrite nine piece image painting code

Source/core/paint/NinePieceImagePainter.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 NinePieceImagePainter_h
 #define NinePieceImagePainter_h
 
-#include "platform/LayoutUnit.h"
 #include "platform/heap/Heap.h"
 #include "third_party/skia/include/core/SkXfermode.h"
 
 namespace blink {
 
 class ComputedStyle;
 class GraphicsContext;
 class LayoutBoxModelObject;
 class LayoutRect;
 class NinePieceImage;
-class BorderImageLength;
 
 class NinePieceImagePainter {
     STACK_ALLOCATED();
 public:
     NinePieceImagePainter(LayoutBoxModelObject&);
 
     bool paint(GraphicsContext*, const LayoutRect&, const ComputedStyle&, const NinePieceImage&, SkXfermode::Mode) const;
 
 private:
-    static LayoutUnit computeBorderImageSide(const BorderImageLength& borderSlice, LayoutUnit borderSide, LayoutUnit imageSide, LayoutUnit boxExtent);
-
     LayoutBoxModelObject& m_layoutObject;
 };
 
 } // namespace blink
 
 #endif // NinePieceImagePainter_h