[Slimming paint] [New Multicolumn] Repaint column rules when they change.

Source/core/paint/MultiColumnSetPainter.cpp

Index: Source/core/paint/MultiColumnSetPainter.cpp
diff --git a/Source/core/paint/MultiColumnSetPainter.cpp b/Source/core/paint/MultiColumnSetPainter.cpp
index 5ece07a06bc5ce93023e81aa5e5544dbbb572625..fb15dfa580a4bc8b107fd239f17307eca96734c6 100644
--- a/Source/core/paint/MultiColumnSetPainter.cpp
+++ b/Source/core/paint/MultiColumnSetPainter.cpp
@@ -52,6 +52,9 @@ void MultiColumnSetPainter::paintColumnRules(const PaintInfo& paintInfo, const L
         return;
 
     DrawingRecorder drawingRecorder(paintInfo.context, m_renderMultiColumnSet.displayItemClient(), DisplayItem::ColumnRules, m_renderMultiColumnSet.visualOverflowRect());
+    if (drawingRecorder.canUseCachedDrawing())
+        return;
+
     bool antialias = BoxPainter::shouldAntialiasLines(paintInfo.context);
     bool leftToRight = m_renderMultiColumnSet.style()->isLeftToRightDirection();
     LayoutUnit currLogicalLeftOffset = leftToRight ? LayoutUnit() : m_renderMultiColumnSet.contentLogicalWidth();