Add ShowLayoutOpportunityTree to NGLayoutOpportunityIterator

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NGLayoutOpportunityTreeNode_h
 #define NGLayoutOpportunityTreeNode_h
 
 #include "core/layout/ng/geometry/ng_edge.h"
 #include "core/layout/ng/geometry/ng_logical_rect.h"
 #include "core/layout/ng/ng_exclusion.h"
@@ skipping 30 matching lines @@
   // Edge that limits this layout opportunity from above.
   NGEdge exclusion_edge;
 
   // Exclusion that splits apart this layout opportunity.
   const NGExclusion* exclusion;  // Not owned.
 
   // Whether this node is a leaf node.
   // The node is a leaf if it doesn't have an exclusion that splits it apart.
   bool IsLeafNode() const { return !exclusion; }
 
+  String ToString() const;
+
   DECLARE_TRACE();
 };
 
+inline std::ostream& operator<<(std::ostream& stream,
+                                const NGLayoutOpportunityTreeNode& value) {
+  return stream << value.ToString();
+}
+
+inline std::ostream& operator<<(std::ostream& out,
+                                const NGLayoutOpportunityTreeNode* value) {
+  return out << (value ? value->ToString() : "(null)");
+}
+
 }  // namespace blink
 #endif  // NGLayoutOpportunityTreeNode_h