Add base::FeatureParam<> struct

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 8832aed550217336f78ebaea7414d73046e12712..e90332992be4366dd48eb4385402dc2dbc977c51 100644
--- a/components/ntp_snippets/features.h
+++ b/components/ntp_snippets/features.h
@@ -9,6 +9,7 @@
 #include <string>
 
 #include "base/feature_list.h"
+#include "base/metrics/field_trial_params.h"
 #include "components/ntp_snippets/category_rankers/category_ranker.h"
 #include "components/prefs/pref_service.h"
 
@@ -39,17 +40,13 @@ extern const base::Feature kCategoryRanker;
 extern const base::Feature kPublisherFaviconsFromNewServerFeature;
 
 // Parameter and its values for the kCategoryRanker feature flag.
-extern const char kCategoryRankerParameter[];
-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();
+extern const char kCategoryRankerConstantRanker[];
+extern const char kCategoryRankerClickBasedRanker[];
+extern const base::FeatureParam<CategoryRankerChoice> kCategoryRankerParameter;
 
 // Builds a CategoryRanker according to kCategoryRanker feature.
 std::unique_ptr<CategoryRanker> BuildSelectedCategoryRanker(
@@ -60,14 +57,13 @@ std::unique_ptr<CategoryRanker> BuildSelectedCategoryRanker(
 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,
 };
+extern const char kCategoryOrderGeneral[];
+extern const char kCategoryOrderEmergingMarketsOriented[];
+extern const base::FeatureParam<CategoryOrderChoice> kCategoryOrderParameter;
 
 // Returns which category order to use according to kCategoryOrder feature.
 CategoryOrderChoice GetSelectedCategoryOrder();