[NTP::SectionOrder] Implement click counts decay.

components/ntp_snippets/features.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/ntp_snippets/features.h"
 
+#include "base/time/clock.h"
 #include "components/ntp_snippets/category_rankers/click_based_category_ranker.h"
 #include "components/ntp_snippets/category_rankers/constant_category_ranker.h"
 #include "components/variations/variations_associated_data.h"
 
 namespace ntp_snippets {
 
 const base::Feature kArticleSuggestionsFeature{
     "NTPArticleSuggestions", base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kBookmarkSuggestionsFeature{
@@ skipping 51 matching lines @@
   if (category_ranker_value == kCategoryRankerClickBasedRanker) {
     return CategoryRankerChoice::CLICK_BASED;
   }
 
   NOTREACHED() << "The " << kCategoryRankerParameter << " parameter value is '"
                << category_ranker_value << "'";
   return CategoryRankerChoice::CONSTANT;
 }
 
 std::unique_ptr<CategoryRanker> BuildSelectedCategoryRanker(
-    PrefService* pref_service) {
+    PrefService* pref_service,
+    std::unique_ptr<base::Clock> clock) {
   CategoryRankerChoice choice = ntp_snippets::GetSelectedCategoryRanker();
   switch (choice) {
     case CategoryRankerChoice::CONSTANT:
       return base::MakeUnique<ConstantCategoryRanker>();
     case CategoryRankerChoice::CLICK_BASED:
-      return base::MakeUnique<ClickBasedCategoryRanker>(pref_service);
+      return base::MakeUnique<ClickBasedCategoryRanker>(pref_service,
+                                                        std::move(clock));
     default:
       NOTREACHED() << "The category ranker choice value is "
                    << static_cast<int>(choice);
   }
   return nullptr;
 }
 
 }  // namespace ntp_snippets