Add other variations (with ids) for NTPSnippets to chrome://flags

chrome/browser/about_flags.h

Index: chrome/browser/about_flags.h
diff --git a/chrome/browser/about_flags.h b/chrome/browser/about_flags.h
index b9907b8ce62cd89aede8510af6608da585afdc81..527a9ed67adfb52cd4f97c96a340755227dfac7d 100644
--- a/chrome/browser/about_flags.h
+++ b/chrome/browser/about_flags.h
@@ -38,8 +38,10 @@ void ConvertFlagsToSwitches(flags_ui::FlagsStorage* flags_storage,
 // Registers variations parameter values selected for features in about:flags.
 // The selected flags are retrieved from |flags_storage|, the registered
 // variation parameters are connected to their corresponding features in
-// |feature_list|.
-void RegisterAllFeatureVariationParameters(
+// |feature_list|. Returns the (possibly empty) comma separated list of
+// additional variation ids to register in the MetricsService that come from
+// variations selected using chrome://flags.
+std::string RegisterAllFeatureVariationParameters(
     flags_ui::FlagsStorage* flags_storage,
     base::FeatureList* feature_list);