Let the RenderFlowThread layer have an empty size.

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index 63e83e3d8eff1a0b96387ac499894f9d9a82d102..761898f2c75ea29bca131a53973154ea57353c18 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -3147,6 +3147,12 @@ LayoutRect RenderLayer::boundingBoxForCompositing(const RenderLayer* ancestorLay
     if (isRootLayer())
         return m_renderer->view()->unscaledDocumentRect();
 
+    // The layer created for the RenderFlowThread is just a helper for painting and should not

[mstensho (USE GERRIT), 2014/09/30 09:10:20]

painting and hit-testing

[rune, 2014/09/30 09:16:19]

Done.

+    // contribute to the bounding box. The RenderMultiColumnSets will contribute the correct
+    // size for the rendered content of the flow thread.

[mstensho (USE GERRIT), 2014/09/30 09:10:20]

s/flow thread/multicol container/

[rune, 2014/09/30 09:16:19]

Done.

+    if (useRegionBasedColumns() && renderer()->isRenderFlowThread())
+        return LayoutRect();
+
     const bool shouldIncludeTransform = paintsWithTransform(PaintBehaviorNormal) || (options == ApplyBoundsChickenEggHacks && transform());
 
     LayoutRect localClipRect = clipper().localClipRect();