[NTP::SectionOrder] Enable ClickBased ranker by default.

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"
@@ skipping 43 matching lines @@
 const char kCategoryRankerConstantRanker[] = "constant";
 const char kCategoryRankerClickBasedRanker[] = "click_based";
 
 CategoryRankerChoice GetSelectedCategoryRanker() {
   std::string category_ranker_value =
       variations::GetVariationParamValueByFeature(kCategoryRanker,
                                                   kCategoryRankerParameter);
 
   if (category_ranker_value.empty()) {
     // Default, Enabled or Disabled.
-    return CategoryRankerChoice::CONSTANT;
+    return CategoryRankerChoice::CLICK_BASED;
   }
   if (category_ranker_value == kCategoryRankerConstantRanker) {
     return CategoryRankerChoice::CONSTANT;
   }
   if (category_ranker_value == kCategoryRankerClickBasedRanker) {
     return CategoryRankerChoice::CLICK_BASED;
   }
 
   NOTREACHED() << "The " << kCategoryRankerParameter << " parameter value is '"
                << category_ranker_value << "'";
@@ skipping 11 matching lines @@
       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