[NTP::SectionOrder] Implement click counts decay.

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 8991367c84965770d38cf008dbb68c93a199ce6c..6ae8eabbefc6127be4e5352b352213f8a6dca1e1 100644
--- a/components/ntp_snippets/features.h
+++ b/components/ntp_snippets/features.h
@@ -12,6 +12,10 @@
 #include "components/ntp_snippets/category_rankers/category_ranker.h"
 #include "components/prefs/pref_service.h"
 
+namespace base {
+class Clock;
+}
+
 namespace ntp_snippets {
 
 // Features to turn individual providers/categories on/off.
@@ -63,7 +67,8 @@ CategoryRankerChoice GetSelectedCategoryRanker();
 
 // Builds a CategoryRanker according to kCategoryRanker feature.
 std::unique_ptr<CategoryRanker> BuildSelectedCategoryRanker(
-    PrefService* pref_service);
+    PrefService* pref_service,
+    std::unique_ptr<base::Clock> clock);
 
 }  // namespace ntp_snippets