[NTP::SectionOrder] Add ranker section to snippets internals.

components/ntp_snippets/category_rankers/category_ranker.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 COMPONENTS_NTP_SNIPPETS_CATEGORY_RANKERS_CATEGORY_RANKER_H_
 #define COMPONENTS_NTP_SNIPPETS_CATEGORY_RANKERS_CATEGORY_RANKER_H_
 
+#include <string>
+#include <vector>
+
 #include "base/time/time.h"
 #include "components/ntp_snippets/category.h"
 
 namespace ntp_snippets {
 
 // Orders categories.
 // The order may be dynamic and change at any time.
 class CategoryRanker {
  public:
   virtual ~CategoryRanker() = default;
@@ skipping 14 matching lines @@
   // If |category_to_insert| has not been added previously, it is added before
   // |anchor|, otherwise nothing is changed.
   virtual void InsertCategoryBeforeIfNecessary(Category category_to_insert,
                                                Category anchor) = 0;
 
   // If |category_to_insert| has not been added previously, it is added after
   // |anchor|, otherwise nothing is changed.
   virtual void InsertCategoryAfterIfNecessary(Category category_to_insert,
                                               Category anchor) = 0;
 
+  struct DebugDataItem {
+    std::string label;
+    std::string content;
+    DebugDataItem(const std::string& label, const std::string& content)
+        : label(label), content(content) {}
+  };
+
+  // Returns DebugData in form of pairs of strings (label; content),
+  // e.g. describing internal state or parameter values.
+  virtual std::vector<DebugDataItem> GetDebugData() = 0;
+
   // Feedback data from the user to update the ranking.
 
   // Called whenever a suggestion is opened by the user.
   virtual void OnSuggestionOpened(Category category) = 0;
 
   // Called whenever a category is dismissed by the user.
   virtual void OnCategoryDismissed(Category category) = 0;
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CATEGORY_RANKERS_CATEGORY_RANKER_H_