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

ios/chrome/browser/about_flags.h

 // Copyright 2013 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.
 
 // Implementation of about_flags for iOS that sets flags based on experimental
 // settings.
 
 #ifndef IOS_CHROME_BROWSER_ABOUT_FLAGS_H_
 #define IOS_CHROME_BROWSER_ABOUT_FLAGS_H_
 
 #include <stddef.h>
+#include <string>
+#include <vector>
 
 #include "components/flags_ui/flags_state.h"
 
 namespace base {
 class CommandLine;
 class ListValue;
 }
 
 namespace flags_ui {
 class FlagsStorage;
 }
 
 // Reads the state from |flags_storage| and adds the command line flags
 // belonging to the active feature entries to |command_line| in addition
 // to the flags from experimental settings.
 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|.
 void GetFlagFeatureEntries(flags_ui::FlagsStorage* flags_storage,
                            flags_ui::FlagAccess access,
                            base::ListValue* supported_entries,
                            base::ListValue* unsupported_entries);
 
 // Enables or disables the current with id |internal_name|.
 void SetFeatureEntryEnabled(flags_ui::FlagsStorage* flags_storage,
                             const std::string& internal_name,
                             bool enable);
 
 // Reset all flags to the default state by clearing all flags.
 void ResetAllFlags(flags_ui::FlagsStorage* flags_storage);
 
 namespace testing {
 
 // Returns the global set of feature entries.
 const flags_ui::FeatureEntry* GetFeatureEntries(size_t* count);
 
 }  // namespace testing
 
 #endif  // IOS_CHROME_BROWSER_ABOUT_FLAGS_H_