Factor painting code out of RenderBox into a new class called BoxPainter.

Source/core/rendering/style/BorderEdge.h

+// Copyright 2014 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 BorderEdge_h
+#define BorderEdge_h
+
+#include "core/rendering/style/RenderStyleConstants.h"
+#include "platform/graphics/Color.h"
+
+namespace blink {
+
+struct BorderEdge {
+    BorderEdge(int edgeWidth, const Color& edgeColor, EBorderStyle edgeStyle, bool edgeIsTransparent, bool edgeIsPresent = true);
+    BorderEdge();
+
+    bool hasVisibleColorAndStyle() const;
+    bool shouldRender() const;
+    bool presentButInvisible() const;
+    bool obscuresBackgroundEdge(float scale) const;
+    bool obscuresBackground() const;
+    int usedWidth() const;
+
+    void getDoubleBorderStripeWidths(int& outerWidth, int& innerWidth) const;
+
+    bool sharesColorWith(const BorderEdge& other) const;
+
+    EBorderStyle borderStyle() const  { return static_cast<EBorderStyle>(style); }
+
+    int width;
+    Color color;
+    bool isTransparent;
+    bool isPresent;
+
+private:
+    unsigned style: 4; // EBorderStyle
+};
+
+} // namespace blink
+
+#endif // BorderEdge_h