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

Source/core/rendering/style/BorderEdge.cpp

+// 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.
+
+#include "config.h"
+#include "core/rendering/style/BorderEdge.h"
+
+namespace blink {
+
+BorderEdge::BorderEdge(int edgeWidth, const Color& edgeColor, EBorderStyle edgeStyle, bool edgeIsTransparent, bool edgeIsPresent)
+    : width(edgeWidth)
+    , color(edgeColor)
+    , isTransparent(edgeIsTransparent)
+    , isPresent(edgeIsPresent)
+    , style(edgeStyle)
+{
+    if (style == DOUBLE && edgeWidth < 3)
+        style = SOLID;
+}
+
+BorderEdge::BorderEdge()
+    : width(0)
+    , isTransparent(false)
+    , isPresent(false)
+    , style(BHIDDEN)
+{
+}
+
+bool BorderEdge::hasVisibleColorAndStyle() const
+{
+    return style > BHIDDEN && !isTransparent;
+}
+
+bool BorderEdge::shouldRender() const { return isPresent && width && hasVisibleColorAndStyle(); }
+bool BorderEdge::presentButInvisible() const { return usedWidth() && !hasVisibleColorAndStyle(); }
+bool BorderEdge::obscuresBackgroundEdge(float scale) const
+{
+    if (!isPresent || isTransparent || (width * scale) < 2 || color.hasAlpha() || style == BHIDDEN)
+        return false;
+
+    if (style == DOTTED || style == DASHED)
+        return false;
+
+    if (style == DOUBLE)
+        return width >= 5 * scale; // The outer band needs to be >= 2px wide at unit scale.
+
+    return true;
+}
+bool BorderEdge::obscuresBackground() const
+{
+    if (!isPresent || isTransparent || color.hasAlpha() || style == BHIDDEN)
+        return false;
+
+    if (style == DOTTED || style == DASHED || style == DOUBLE)
+        return false;
+
+    return true;
+}
+
+int BorderEdge::usedWidth() const
+{
+    return isPresent ? width : 0;
+}
+
+void BorderEdge::getDoubleBorderStripeWidths(int& outerWidth, int& innerWidth) const
+{
+    int fullWidth = usedWidth();
+    outerWidth = fullWidth / 3;
+    innerWidth = fullWidth * 2 / 3;
+
+    // We need certain integer rounding results
+    if (fullWidth % 3 == 2)
+        outerWidth += 1;
+
+    if (fullWidth % 3 == 1)
+        innerWidth += 1;
+}
+
+bool BorderEdge::sharesColorWith(const BorderEdge& other) const
+{
+    return color == other.color;
+}
+
+} // namespace blink