[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..61c8f4c636c97f1bf115c78b598c0aa4f3c7de05 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"
@@ -87,4 +88,37 @@ std::unique_ptr<CategoryRanker> BuildSelectedCategoryRanker(
   return nullptr;
 }
 
+const base::Feature kCategoryOrder{"ContentSuggestionsCategoryOrder",
+                                   base::FEATURE_DISABLED_BY_DEFAULT};
+
+extern const char kCategoryOrderParameter[] = "category_order";
+extern const char kCategoryOrderGeneral[] = "general";
+extern const char kCategoryOrderEmergingMarketsOriented[] =

[Marc Treib, 2017/02/13 14:25:23]

No "extern" here (does it work like this?!)

[vitaliii, 2017/02/14 09:32:32]

Done.

It did work like that.

+    "emerging_markets_oriented";
+
+CategoryOrderChoice GetSelectedCategoryOrder() {
+  std::string category_order_value =

[Marc Treib, 2017/02/13 14:25:23]

nit: Move this after the check if the feature is enabled

[vitaliii, 2017/02/14 09:32:32]

Done.

+      variations::GetVariationParamValueByFeature(kCategoryOrder,
+                                                  kCategoryOrderParameter);
+
+  if (!base::FeatureList::IsEnabled(kCategoryOrder)) {
+    return CategoryOrderChoice::GENERAL;
+  }
+
+  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;
+  }
+
+  NOTREACHED() << "The " << kCategoryOrderParameter << " parameter value is '"

[Marc Treib, 2017/02/13 14:25:23]

This shouldn't be a NOTREACHED - getting an invalid input parameter is not a bug
in Chrome. LOG(DFATAL) would be okay if you want.

[vitaliii, 2017/02/14 09:32:32]

Done.

+               << category_order_value << "'";
+  return CategoryOrderChoice::GENERAL;
+}
+
 }  // namespace ntp_snippets