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

chrome/browser/about_flags.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_BROWSER_ABOUT_FLAGS_H_
 #define CHROME_BROWSER_ABOUT_FLAGS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 20 matching lines @@
 
 // Reads the state from |flags_storage| and adds the command line flags
 // belonging to the active feature entries to |command_line|.
 void ConvertFlagsToSwitches(flags_ui::FlagsStorage* flags_storage,
                             base::CommandLine* command_line,
                             flags_ui::SentinelsMode sentinels);
 
 // 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);
 
 // Compares a set of switches of the two provided command line objects and
 // returns true if they are the same and false otherwise.
 // If |out_difference| is not NULL, it's filled with set_symmetric_difference
 // between sets.
 bool AreSwitchesIdenticalToCurrentCommandLine(
     const base::CommandLine& new_cmdline,
     const base::CommandLine& active_cmdline,
@@ skipping 45 matching lines @@
 
 // This value is reported as switch histogram ID if switch name has unknown
 // format.
 extern const base::HistogramBase::Sample kBadSwitchFormatHistogramId;
 
 }  // namespace testing
 
 }  // namespace about_flags
 
 #endif  // CHROME_BROWSER_ABOUT_FLAGS_H_