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

ios/chrome/browser/about_flags.h

Index: ios/chrome/browser/about_flags.h
diff --git a/ios/chrome/browser/about_flags.h b/ios/chrome/browser/about_flags.h
index a9fdcc56b48205eae13b8a7c0cef0334e3324ef1..a9b894bfd4b6f8d917253110543b1d0f5b72cd54 100644
--- a/ios/chrome/browser/about_flags.h
+++ b/ios/chrome/browser/about_flags.h
@@ -9,6 +9,8 @@
 #define IOS_CHROME_BROWSER_ABOUT_FLAGS_H_
 
 #include <stddef.h>
+#include <string>
+#include <vector>
 
 #include "components/flags_ui/flags_state.h"
 
@@ -27,6 +29,16 @@ class FlagsStorage;
 void ConvertFlagsToSwitches(flags_ui::FlagsStorage* flags_storage,
                             base::CommandLine* command_line);
 
+// 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|. Returns the (possibly empty) list of additional variation ids
+// to register in the MetricsService that come from variations selected using
+// chrome://flags.
+std::vector<std::string> RegisterAllFeatureVariationParameters(
+    flags_ui::FlagsStorage* flags_storage,
+    base::FeatureList* feature_list);
+
 // Gets the list of feature entries. Entries that are available for the current
 // platform are appended to |supported_entries|; all other entries are appended
 // to |unsupported_entries|.