The default render object layout implementation is dead code

Source/core/rendering/RenderObject.h

Index: Source/core/rendering/RenderObject.h
diff --git a/Source/core/rendering/RenderObject.h b/Source/core/rendering/RenderObject.h
index 7034ad7589ea8a4692054474d86583df7d249ccd..aad27d20daac37f959076a9ca2ba1d66a6bd593c 100644
--- a/Source/core/rendering/RenderObject.h
+++ b/Source/core/rendering/RenderObject.h
@@ -665,8 +665,9 @@ public:
 
     virtual void paint(PaintInfo&, const LayoutPoint&);
 
-    // Recursive function that computes the size and position of this object and all its descendants.
-    virtual void layout();
+    // Subclasses must reimplement this method to compute the size and position
+    // of this object and all its descendants.
+    virtual void layout() = 0;
     virtual void didLayout(ResourceLoadPriorityOptimizer&);
     virtual void didScroll(ResourceLoadPriorityOptimizer&);