[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 03cfbc3bf45f0831f3d6c9836aa39d7f2e8254df..fb6a1937cbde9f972f7c595e51450a024269d642 100644
--- a/components/ntp_snippets/features.cc
+++ b/components/ntp_snippets/features.cc
@@ -44,4 +44,7 @@ const base::Feature kFetchMoreFeature{"NTPSuggestionsFetchMore",
 const base::Feature kPreferAmpUrlsFeature{"NTPPreferAmpUrls",
                                           base::FEATURE_ENABLED_BY_DEFAULT};
 
+const base::Feature kCategoryRanker{"NTPCategoryRanker",
+                                    base::FEATURE_ENABLED_BY_DEFAULT};
+
 }  // namespace ntp_snippets