[NTP Snippets] Metrics: switch over known categories

components/ntp_snippets/category.cc

 // 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.
 
 #include "components/ntp_snippets/category.h"
 
+#include "base/logging.h"
+
 namespace ntp_snippets {
 
 Category::Category(int id) : id_(id) {}
 
 bool Category::IsKnownCategory(KnownCategories known_category) const {
+  DCHECK_NE(known_category, KnownCategories::LOCAL_CATEGORIES_COUNT);
+  DCHECK_NE(known_category, KnownCategories::REMOTE_CATEGORIES_OFFSET);
   return id_ == static_cast<int>(known_category);
 }
 
 bool operator==(const Category& left, const Category& right) {
   return left.id() == right.id();
 }
 
 bool operator!=(const Category& left, const Category& right) {
   return !(left == right);
 }
 
 bool Category::CompareByID::operator()(const Category& left,
                                        const Category& right) const {
   return left.id() < right.id();
 }
 
 std::ostream& operator<<(std::ostream& os, const Category& obj) {
   os << obj.id();
   return os;
 }
 
 }  // namespace ntp_snippets