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

components/ntp_snippets/features.cc

Index: components/ntp_snippets/features.cc
diff --git a/components/ntp_snippets/features.cc b/components/ntp_snippets/features.cc
index 085257bc24d4cb05859a7827ee3313290e0dbfc7..5550d947bd7789ae064dbed34013737cf03c77ce 100644
--- a/components/ntp_snippets/features.cc
+++ b/components/ntp_snippets/features.cc
@@ -41,4 +41,7 @@ const base::Feature kForeignSessionsSuggestionsFeature{
 const base::Feature kFetchMoreFeature{"NTPSuggestionsFetchMore",
                                       base::FEATURE_ENABLED_BY_DEFAULT};
 
+const base::Feature kCategoryRanker{"NTPCategoryRanker",
+                                    base::FEATURE_ENABLED_BY_DEFAULT};
+
 }  // namespace ntp_snippets