Compute better reference/visual boxes for clip-path in columns

third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
index 7cd8c1ffc74a79b448471d79ba77b9736bc8a7ff..bfafa3ed3681b9113457be170ba49cf7b0544161 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
@@ -268,9 +268,14 @@ PaintLayerPainter::PaintResult PaintLayerPainter::paintLayerContents(GraphicsCon
         paintingInfo.ancestorHasClipPathClipping = true;
 
         LayoutRect referenceBox(m_paintLayer.boxForClipPath());
-        referenceBox.moveBy(offsetFromRoot);
+        // Note that this isn't going to work correctly if crossing a column boundary. The reference box should be
+        // determined per-fragment, and hence this ought to be perform after fragmentation.

[mstensho (USE GERRIT), 2016/09/02 19:44:09]

*performed

[fs, 2016/09/02 20:12:01]

Fixed, thanks.

+        if (m_paintLayer.enclosingPaginationLayer())
+            m_paintLayer.convertFromFlowThreadToVisualBoundingBoxInAncestor(paintingInfo.rootLayer, referenceBox);
+        else
+            referenceBox.moveBy(offsetFromRoot);
         clipPathClipper.emplace(
-            context, *m_paintLayer.layoutObject(), FloatRect(referenceBox), FloatPoint(offsetFromRoot));
+            context, *m_paintLayer.layoutObject(), FloatRect(referenceBox), FloatPoint(referenceBox.location()));
     }
 
     Optional<CompositingRecorder> compositingRecorder;