[NTP::SectionOrder] Add EM oriented order.

components/ntp_snippets/features.h

Index: components/ntp_snippets/features.h
diff --git a/components/ntp_snippets/features.h b/components/ntp_snippets/features.h
index cc8be99fdf3029c92d1994fda4b148c1c0d31ce2..3ef1800d7293fdd9d9bb94009535f23a9ae28f22 100644
--- a/components/ntp_snippets/features.h
+++ b/components/ntp_snippets/features.h
@@ -46,9 +46,8 @@ 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[];
 
@@ -65,6 +64,21 @@ 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;
+
+extern const char kCategoryOrderParameter[];

[Marc Treib, 2017/02/13 14:25:23]

Comment, similar to CategoryRanker above?

[vitaliii, 2017/02/14 09:32:32]

Done.

+extern const char kCategoryOrderGeneral[];
+extern const char kCategoryOrderEmergingMarketsOriented[];
+
+enum class CategoryOrderChoice {
+  GENERAL,

[Marc Treib, 2017/02/13 14:25:23]

DEFAULT?

[vitaliii, 2017/02/14 09:32:32]

I thought about this.
These orders may be used in ClickBasedRanker as a default (initial) order, so I
was reluctant to name one of these orders "DEFAULT". Overall, neither default
nor general are that informative.

+  EMERGING_MARKETS_ORIENTED,
+};
+
+// Returns which category order to use according to kCategoryOrder feature.
+CategoryOrderChoice GetSelectedCategoryOrder();
+
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_FEATURES_H_