[New Multicolumn] Add support for column-span:all

Source/core/rendering/RenderPagedFlowThread.h

Index: Source/core/rendering/RenderPagedFlowThread.h
diff --git a/Source/core/rendering/RenderPagedFlowThread.h b/Source/core/rendering/RenderPagedFlowThread.h
index da41adc708cd17c64735f96e353a4a160be8427f..a71d4a6f96fb8ee7702aa672bc6db7c488ccf6af 100644
--- a/Source/core/rendering/RenderPagedFlowThread.h
+++ b/Source/core/rendering/RenderPagedFlowThread.h
@@ -20,11 +20,13 @@ public:
     RenderBlockFlow* pagedBlockFlow() const { return toRenderBlockFlow(parent()); }
 
     virtual bool isRenderPagedFlowThread() const override { return true; }
-    virtual bool heightIsAuto() const override { return !columnHeightAvailable(); }
     virtual const char* renderName() const override;
     virtual bool needsNewWidth() const override;
     virtual void updateLogicalWidth() override;
     virtual void layout();
+
+private:
+    virtual bool isDescendantValidColumnSpanner(RenderObject* /*descendant*/) const override { return false; }
 };
 
 } // namespace blink