[NTP::SectionOrder] Add EM oriented order.

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 8c40e5a70d7e4815b61857488bc5332296c79aaf..85b325f5f3e62ef27b622b45b784bb7796a1f5bc 100644
--- a/components/ntp_snippets/features.cc
+++ b/components/ntp_snippets/features.cc
@@ -4,6 +4,7 @@
 
 #include "components/ntp_snippets/features.h"
 
+#include "base/feature_list.h"
 #include "base/memory/ptr_util.h"
 #include "base/time/clock.h"
 #include "components/ntp_snippets/category_rankers/click_based_category_ranker.h"
@@ -65,8 +66,8 @@ CategoryRankerChoice GetSelectedCategoryRanker() {
     return CategoryRankerChoice::CLICK_BASED;
   }
 
-  NOTREACHED() << "The " << kCategoryRankerParameter << " parameter value is '"
-               << category_ranker_value << "'";
+  LOG(DFATAL) << "The " << kCategoryRankerParameter << " parameter value is '"
+              << category_ranker_value << "'";
   return CategoryRankerChoice::CONSTANT;
 }
 
@@ -80,11 +81,41 @@ std::unique_ptr<CategoryRanker> BuildSelectedCategoryRanker(
     case CategoryRankerChoice::CLICK_BASED:
       return base::MakeUnique<ClickBasedCategoryRanker>(pref_service,
                                                         std::move(clock));
-    default:
-      NOTREACHED() << "The category ranker choice value is "
-                   << static_cast<int>(choice);
   }
   return nullptr;
 }
 
+const base::Feature kCategoryOrder{"ContentSuggestionsCategoryOrder",
+                                   base::FEATURE_DISABLED_BY_DEFAULT};
+
+const char kCategoryOrderParameter[] = "category_order";
+const char kCategoryOrderGeneral[] = "general";
+const char kCategoryOrderEmergingMarketsOriented[] =
+    "emerging_markets_oriented";
+
+CategoryOrderChoice GetSelectedCategoryOrder() {
+  if (!base::FeatureList::IsEnabled(kCategoryOrder)) {
+    return CategoryOrderChoice::GENERAL;
+  }
+
+  std::string category_order_value =
+      variations::GetVariationParamValueByFeature(kCategoryOrder,
+                                                  kCategoryOrderParameter);
+
+  if (category_order_value.empty()) {
+    // Enabled with no parameters.
+    return CategoryOrderChoice::GENERAL;
+  }
+  if (category_order_value == kCategoryOrderGeneral) {
+    return CategoryOrderChoice::GENERAL;
+  }
+  if (category_order_value == kCategoryOrderEmergingMarketsOriented) {
+    return CategoryOrderChoice::EMERGING_MARKETS_ORIENTED;
+  }
+
+  LOG(DFATAL) << "The " << kCategoryOrderParameter << " parameter value is '"
+              << category_order_value << "'";
+  return CategoryOrderChoice::GENERAL;
+}
+
 }  // namespace ntp_snippets