[NTP::SectionOrder] Add EM oriented order.

components/ntp_snippets/features.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_FEATURES_H_
 #define COMPONENTS_NTP_SNIPPETS_FEATURES_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 28 matching lines @@
 
 // Feature to allow UI as specified here: https://crbug.com/660837.
 extern const base::Feature kIncreasedVisibility;
 
 // Feature to prefer AMP URLs over regular URLs when available.
 extern const base::Feature kPreferAmpUrlsFeature;
 
 // Feature to choose a category ranker.
 extern const base::Feature kCategoryRanker;
 
-// Parameter for a kCategoryRanker feature flag.
+// Parameter and its values for the kCategoryRanker feature flag.
 extern const char kCategoryRankerParameter[];
-// Possible values of the parameter above.
 extern const char kCategoryRankerConstantRanker[];
 extern const char kCategoryRankerClickBasedRanker[];
 
 enum class CategoryRankerChoice {
   CONSTANT,
   CLICK_BASED,
 };
 
 // Returns which CategoryRanker to use according to kCategoryRanker feature.
 CategoryRankerChoice GetSelectedCategoryRanker();
 
 // Builds a CategoryRanker according to kCategoryRanker feature.
 std::unique_ptr<CategoryRanker> BuildSelectedCategoryRanker(
     PrefService* pref_service,
     std::unique_ptr<base::Clock> clock);
 
+// Feature to choose a default category order.
+extern const base::Feature kCategoryOrder;
+
+// Parameter and its values for the kCategoryOrder feature flag.
+extern const char kCategoryOrderParameter[];
+extern const char kCategoryOrderGeneral[];
+extern const char kCategoryOrderEmergingMarketsOriented[];
+
+enum class CategoryOrderChoice {
+  GENERAL,
+  EMERGING_MARKETS_ORIENTED,
+};
+
+// Returns which category order to use according to kCategoryOrder feature.
+CategoryOrderChoice GetSelectedCategoryOrder();
+
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_FEATURES_H_