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

Source/core/paint/BoxPainter.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 BoxPainter_h
+#define BoxPainter_h
+
+#include "core/rendering/RenderBoxModelObject.h"
+
+namespace blink {
+
+class LayoutPoint;
+struct PaintInfo;
+class RenderBox;
+class RenderObject;
+
+class BoxPainter {
+public:
+    BoxPainter(RenderBox& renderBox) : m_renderBox(renderBox) { }
+    void paint(PaintInfo&, const LayoutPoint&);
+
+    void paintBoxDecorationBackground(PaintInfo&, const LayoutPoint&);
+    void paintMask(PaintInfo&, const LayoutPoint&);
+    void paintClippingMask(PaintInfo&, const LayoutPoint&);
+    void paintFillLayers(const PaintInfo&, const Color&, const FillLayer&, const LayoutRect&, BackgroundBleedAvoidance = BackgroundBleedNone, CompositeOperator = CompositeSourceOver, RenderObject* backgroundObject = 0);
+    void paintMaskImages(const PaintInfo&, const LayoutRect&);
+    void paintBoxDecorationBackgroundWithRect(PaintInfo&, const LayoutPoint&, const LayoutRect&);
+
+private:
+    void paintBackground(const PaintInfo&, const LayoutRect&, const Color& backgroundColor, BackgroundBleedAvoidance = BackgroundBleedNone);
+    void paintRootBoxFillLayers(const PaintInfo&);
+    void paintFillLayer(const PaintInfo&, const Color&, const FillLayer&, const LayoutRect&, BackgroundBleedAvoidance, CompositeOperator, RenderObject* backgroundObject, bool skipBaseColor = false);
+
+    // FIXME: this should be const.

[pdr., 2014/09/09 20:45:42]

This effectively bloats RenderBox by 2 references. An alternative is to have
this be a static class and pass "this" in to all functions, but it's ugly.

[chrishtr, 2014/09/09 22:38:18]

It's 1 reference, as we discussed offline. I think it's ok because it's
compatible with the end design of a DisplayObject tree.

+    RenderBox& m_renderBox;
+};
+
+} // namespace blink
+
+#endif