Move NinePieceImage painting to a separate class

Source/core/paint/NinePieceImagePainter.h

Index: Source/core/paint/NinePieceImagePainter.h
diff --git a/Source/core/paint/NinePieceImagePainter.h b/Source/core/paint/NinePieceImagePainter.h
new file mode 100644
index 0000000000000000000000000000000000000000..eb193c73bf71f95b7786fb1a2e5449f006f09d45
--- /dev/null
+++ b/Source/core/paint/NinePieceImagePainter.h
@@ -0,0 +1,34 @@
+// 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 "third_party/skia/include/core/SkXfermode.h"
+
+namespace blink {
+
+class ComputedStyle;
+class GraphicsContext;
+class LayoutBoxModelObject;
+class LayoutRect;
+class NinePieceImage;
+class BorderImageLength;
+
+class NinePieceImagePainter {

[pdr., 2015/06/02 01:41:51]

Can you add STACK_ALLOCATED() here?

[davve, 2015/06/02 07:18:52]

Done.

+public:
+    NinePieceImagePainter(LayoutBoxModelObject&);
+
+    bool paint(GraphicsContext*, const LayoutRect&, const ComputedStyle&, const NinePieceImage&, SkXfermode::Mode);

[pdr., 2015/06/02 01:41:50]

Can you make this const?

Maybe best for a followup but can we refactor this to not return a bool? It only
appears to be used in one questionable-looking place with the comment
"border-image is not affected by border-radius."

[davve, 2015/06/02 07:18:52]

Done.

+
+private:
+    static LayoutUnit computeBorderImageSide(const BorderImageLength& borderSlice, LayoutUnit borderSide, LayoutUnit imageSide, LayoutUnit boxExtent);

[pdr., 2015/06/02 01:41:51]

Nit, maybe for a followup: should these LayoutUnit params be passed as const
references?

[davve, 2015/06/02 07:18:52]

Will look into it in a follow-up.

+
+    LayoutBoxModelObject& m_layoutObject;
+};
+
+} // namespace blink
+
+#endif // NinePieceImagePainter_h