Add ShowLayoutOpportunityTree to NGLayoutOpportunityIterator

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

Index: third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.h b/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.h
index 0e7c0046e64d09102e90ab97f217c529dc1d683c..9ecf8bd40681e00ec62e8ffdcd4452301ce44125 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.h
@@ -38,6 +38,11 @@ class CORE_EXPORT NGLayoutOpportunityIterator final {
   // TODO(chrome-layout-team): Refactor with using C++ <iterator> library.
   const NGLayoutOpportunity Next();
 
+#ifndef NDEBUG
+  // Prints Layout Opportunity tree for debug purposes.
+  void ShowLayoutOpportunityTree() const;
+#endif
+
  private:
   // Mutable Getters.
   NGLayoutOpportunityTreeNode* MutableOpportunityTreeRoot() {