[LayoutNG] Add NGLayoutInputNode::ShowNodeTree

third_party/WebKit/Source/core/layout/ng/ng_layout_input_node.h

Index: third_party/WebKit/Source/core/layout/ng/ng_layout_input_node.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_layout_input_node.h b/third_party/WebKit/Source/core/layout/ng/ng_layout_input_node.h
index 25b30c705c57aabd1a84595cda7872a8ac777d9b..1ca009956329ba579eea408887ba52609da840a3 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_layout_input_node.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_layout_input_node.h
@@ -40,16 +40,22 @@ class CORE_EXPORT NGLayoutInputNode
   virtual NGLayoutInputNode* NextSibling() = 0;
 
   // Returns the LayoutObject which is associated with this node.
-  virtual LayoutObject* GetLayoutObject() = 0;
+  virtual LayoutObject* GetLayoutObject() const = 0;
 
   virtual MinMaxContentSize ComputeMinMaxContentSize() = 0;
 
   virtual const ComputedStyle& Style() const = 0;
 
+  virtual String ToString() const = 0;
+
   NGLayoutInputNodeType Type() const {
     return static_cast<NGLayoutInputNodeType>(type_);
   }
 
+#ifndef NDEBUG
+  void ShowNodeTree() const;
+#endif
+
   DEFINE_INLINE_VIRTUAL_TRACE() {}
 
  protected: