[NTP::SectionOrder] Add a flag to choose category ranker.

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 d4cf6a023d4a9398335fc392b3235c7aa52f524c..ae5c938cb88f5278fb8be15f00c6760d5d27d5fb 100644
--- a/components/ntp_snippets/features.h
+++ b/components/ntp_snippets/features.h
@@ -41,6 +41,21 @@ extern const base::Feature kFetchMoreFeature;
 // 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;
+
+const char kCategoryRankerParameter[] = "category_ranker";

[jkrcal, 2016/12/22 13:39:15]

can you make these extern as well and define them in the .cc file?

[vitaliii, 2016/12/22 13:47:10]

Done.

+const char kCategoryRankerConstantRanker[] = "constant";
+const char kCategoryRankerClickBasedRanker[] = "click_based";
+
+enum class CategoryRankerChoice {
+  CONSTANT,
+  CLICK_BASED,
+};
+
+// Returns which CategoryRanker to use according to kCategoryRanker feature.
+CategoryRankerChoice GetSelectedCategoryRanker();
+
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_FEATURES_H_