Allow overriding variation parameter via chrome://flags.

components/flags_ui/flags_state.h

 // Copyright 2015 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 COMPONENTS_FLAGS_UI_FLAGS_STATE_H_
 #define COMPONENTS_FLAGS_UI_FLAGS_STATE_H_
 
 #include <stddef.h>
 
 #include <map>
 #include <set>
 #include <string>
 
 #include "base/callback_forward.h"
 #include "base/command_line.h"
 #include "base/macros.h"
 
 namespace base {
 class ListValue;
 }
 
+namespace {

[Alexei Svitkine (slow), 2016/06/16 09:40:57]

This is not quite what I meant.

There shouldn't be an anon namespace inside a header file.

Instead, do the following:

// Internal functionality exposed for tests.
namespace internal {
// your comment here
extern const char kTrialGroupAboutFlags[];
}  // namespace internal.

And then define it in the .cc file.

Also, put the above inside of namespace flags_ui.

[jkrcal, 2016/06/16 14:49:17]

Done. 
(Thanks for explaining!)

+// The trial group selected when feature variation parameters are registered via
+// FlagsState::RegisterFeatureVariationParameters().
+const char kTrialGroupAboutFlags[] = "AboutFlags";
+}
+
 namespace flags_ui {
 
 struct FeatureEntry;
 class FlagsStorage;
 struct SwitchEntry;
 
 // Enumeration of OSs.
 enum {
   kOsMac = 1 << 0,
   kOsWin = 1 << 1,
@@ skipping 17 matching lines @@
 // be the ones marked for Apple review (which otherwise will not be shown).
 enum FlagAccess { kGeneralAccessFlagsOnly, kOwnerAccessToFlags,
                   kAppleReviewAccessToFlags };
 
 // Stores and encapsulates the little state that about:flags has.
 class FlagsState {
  public:
   FlagsState(const FeatureEntry* feature_entries, size_t num_feature_entries);
   ~FlagsState();
 
+  // Reads the state from |flags_storage| and adds the command line flags
+  // belonging to the active feature entries to |command_line|. Features are
+  // appended via |enable_features_flag_name| and |disable_features_flag_name|.
   void ConvertFlagsToSwitches(FlagsStorage* flags_storage,
                               base::CommandLine* command_line,
                               SentinelsMode sentinels,
                               const char* enable_features_flag_name,
                               const char* disable_features_flag_name);
   bool IsRestartNeededToCommitChanges();
   void SetFeatureEntryEnabled(FlagsStorage* flags_storage,
                               const std::string& internal_name,
                               bool enable);
   void RemoveFlagsSwitches(
       std::map<std::string, base::CommandLine::StringType>* switch_list);
   void ResetAllFlags(FlagsStorage* flags_storage);
   void Reset();
 
+  // Registers variations parameter values stored in |flags_storage| (previously
+  // selected in about:flags).
+  void RegisterAllFeatureVariationParameters(FlagsStorage* flags_storage);
+
   // 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(
       FlagsStorage* flags_storage,
       FlagAccess access,
       base::ListValue* supported_entries,
       base::ListValue* unsupported_entries,
       base::Callback<bool(const FeatureEntry&)> skip_feature_entry);
 
@@ skipping 75 matching lines @@
   // Map from switch name to a set of string, that keeps track which strings
   // were appended to existing (list value) switches.
   std::map<std::string, std::set<std::string>> appended_switches_;
 
   DISALLOW_COPY_AND_ASSIGN(FlagsState);
 };
 
 }  // namespace flags_ui
 
 #endif  // COMPONENTS_FLAGS_UI_FLAGS_STATE_H_