Implement interfaces in PaintInfo and make it a class.

Source/core/rendering/RenderScrollbarPart.cpp

Index: Source/core/rendering/RenderScrollbarPart.cpp
diff --git a/Source/core/rendering/RenderScrollbarPart.cpp b/Source/core/rendering/RenderScrollbarPart.cpp
index 9d36ccecc3fd7cee98f9cb6de235aa08b90596c6..6fe98c42c392708a9c98e2c3a400dcf5ebe1a305 100644
--- a/Source/core/rendering/RenderScrollbarPart.cpp
+++ b/Source/core/rendering/RenderScrollbarPart.cpp
@@ -186,13 +186,13 @@ void RenderScrollbarPart::paintIntoRect(GraphicsContext* graphicsContext, const
     // Now do the paint.
     PaintInfo paintInfo(graphicsContext, pixelSnappedIntRect(rect), PaintPhaseBlockBackground, PaintBehaviorNormal);
     paint(paintInfo, paintOffset);
-    paintInfo.phase = PaintPhaseChildBlockBackgrounds;
+    paintInfo.setPhase(PaintPhaseChildBlockBackgrounds);
     paint(paintInfo, paintOffset);
-    paintInfo.phase = PaintPhaseFloat;
+    paintInfo.setPhase(PaintPhaseFloat);
     paint(paintInfo, paintOffset);
-    paintInfo.phase = PaintPhaseForeground;
+    paintInfo.setPhase(PaintPhaseForeground);
     paint(paintInfo, paintOffset);
-    paintInfo.phase = PaintPhaseOutline;
+    paintInfo.setPhase(PaintPhaseOutline);
     paint(paintInfo, paintOffset);
 }