[New Multicolumn] Layout support for column-span:all.

Source/core/rendering/RenderBlockFlow.h

Index: Source/core/rendering/RenderBlockFlow.h
diff --git a/Source/core/rendering/RenderBlockFlow.h b/Source/core/rendering/RenderBlockFlow.h
index 312c6ec51bfe8ecc1c25f2d6e0d8e5b2f9343a7b..1c471532847eca0a5f7f28ac73459d12c7c015e6 100644
--- a/Source/core/rendering/RenderBlockFlow.h
+++ b/Source/core/rendering/RenderBlockFlow.h
@@ -48,6 +48,7 @@ class LineBreaker;
 class LineInfo;
 class LineWidth;
 class RenderMultiColumnFlowThread;
+class RenderMultiColumnSpannerPlaceholder;
 class RenderRubyRun;
 template <class Run> class BidiRunList;
 
@@ -202,6 +203,8 @@ public:
     LayoutUnit paginationStrut() const { return m_rareData ? m_rareData->m_paginationStrut : LayoutUnit(); }
     void setPaginationStrut(LayoutUnit);
 
+    void positionSpannerDescendant(RenderMultiColumnSpannerPlaceholder& child);
+
     virtual bool avoidsFloats() const override;
 
     using RenderBoxModelObject::moveChildrenTo;