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 5d1dac39d9f5a8242849cebfb1c6e1ec191fda3f..c88fd26b927d1e6408a8001765897f921afd63e1 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);
 }