[NTP Snippets] Metrics: switch over known categories

components/ntp_snippets/category.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_H_
 #define COMPONENTS_NTP_SNIPPETS_CATEGORY_H_
 
 #include <ostream>
 
 namespace ntp_snippets {
@@ skipping 16 matching lines @@
 
   // Recently used bookmarks.
   BOOKMARKS,
 
   // Physical Web page available in the vicinity.
   PHYSICAL_WEB_PAGES,
 
   // Follows the last local category.
   LOCAL_CATEGORIES_COUNT,
 
+  // Remote categories come after this.
   REMOTE_CATEGORIES_OFFSET = 10000,
 
   // Articles for you.
   ARTICLES,
 };
 
 // A category groups ContentSuggestions which belong together. Use the
 // CategoryFactory to obtain instances.
 class Category {
  public:
   // An arbitrary but consistent ordering. Can be used to look up categories in
   // a std::map, but should not be used to order categories for other purposes.
   struct CompareByID;
 
   // Returns a non-negative identifier that is unique for the category and can
   // be converted back to a Category instance using
   // |CategoryFactory::FromIDValue(id)|.
   // Note that these IDs are not necessarily stable across multiple runs of
   // the application, so they should not be persisted.
   int id() const { return id_; }
 
+  // Returns whether this category matches the given |known_category|.
   bool IsKnownCategory(KnownCategories known_category) const;
 
  private:
   friend class CategoryFactory;
 
   explicit Category(int id);
 
   int id_;
 
   // Allow copy and assignment.
 };
 
 bool operator==(const Category& left, const Category& right);
 
 bool operator!=(const Category& left, const Category& right);
 
 struct Category::CompareByID {
   bool operator()(const Category& left, const Category& right) const;
 };
 
 std::ostream& operator<<(std::ostream& os, const Category& obj);
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CATEGORY_H_