[New Multicolumn] Support for block direction margins on spanners.

Source/core/rendering/RenderBox.cpp

Index: Source/core/rendering/RenderBox.cpp
diff --git a/Source/core/rendering/RenderBox.cpp b/Source/core/rendering/RenderBox.cpp
index baf97ea1909c8c1bea1eabbf22fefc514121a363..2dd1e45b9e36818bf5cf48e1035339ef52db6c8f 100644
--- a/Source/core/rendering/RenderBox.cpp
+++ b/Source/core/rendering/RenderBox.cpp
@@ -256,6 +256,9 @@ void RenderBox::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle
     }
     updateShapeOutsideInfoAfterStyleChange(*style(), oldStyle);
     updateGridPositionAfterStyleChange(oldStyle);
+
+    if (RenderMultiColumnSpannerPlaceholder* placeholder = this->spannerPlaceholder())
+        placeholder->updateMarginProperties();
 }
 
 void RenderBox::updateShapeOutsideInfoAfterStyleChange(const RenderStyle& style, const RenderStyle* oldStyle)