[NTP::SectionOrder] Replace CategoryFactory with a category ranker.

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 {
 
+// static
+Category Category::FromKnownCategory(KnownCategories known_category) {
+  return FromIDValue(static_cast<int>(known_category));
+}
+
+// static
+Category Category::FromRemoteCategory(int remote_category) {
+  DCHECK_GT(remote_category, 0);
+  return Category(static_cast<int>(KnownCategories::REMOTE_CATEGORIES_OFFSET) +
+                  remote_category);
+}
+
+// static
+Category Category::FromIDValue(int id) {
+  DCHECK_GE(id, 0);
+  DCHECK(id < static_cast<int>(KnownCategories::LOCAL_CATEGORIES_COUNT) ||
+         id > static_cast<int>(KnownCategories::REMOTE_CATEGORIES_OFFSET));
+  return Category(id);
+}
+
 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