Avoid stack overflow triggered by out-of-band layout of flexbox child.

Source/core/layout/LayoutFlowThread.h

Index: Source/core/layout/LayoutFlowThread.h
diff --git a/Source/core/layout/LayoutFlowThread.h b/Source/core/layout/LayoutFlowThread.h
index 2a8a546633cefeaa687fe5c4180fe6494a4fc057..2aa7ca0c989e71707e40ffb4ec1ea4c80773b7d4 100644
--- a/Source/core/layout/LayoutFlowThread.h
+++ b/Source/core/layout/LayoutFlowThread.h
@@ -64,11 +64,6 @@ public:
     // can easily avoid drawing the children directly.
     DeprecatedPaintLayerType layerTypeRequired() const final { return NormalDeprecatedPaintLayer; }
 
-    // Skip past a column spanner during flow thread layout. Spanners are not laid out inside the
-    // flow thread, since the flow thread is not in a spanner's containing block chain (since the
-    // containing block is the multicol container).
-    virtual void skipColumnSpanner(LayoutBox*, LayoutUnit logicalTopInFlowThread) { }
-
     virtual void flowThreadDescendantWasInserted(LayoutObject*) { }
     virtual void flowThreadDescendantWillBeRemoved(LayoutObject*) { }
     virtual void flowThreadDescendantStyleWillChange(LayoutObject*, StyleDifference, const ComputedStyle& newStyle) { }