chrome/browser/about_flags.cc

// Copyright (c) 2010 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.

#include "chrome/browser/about_flags.h"

#include <algorithm>
#include <iterator>
#include <map>
#include <set>

#include "app/l10n_util.h"
#include "base/command_line.h"
#include "base/singleton.h"
#include "base/string_number_conversions.h"
#include "base/values.h"
#include "chrome/browser/metrics/user_metrics.h"
#include "chrome/browser/prefs/pref_service.h"
#include "chrome/common/chrome_switches.h"
#include "chrome/common/pref_names.h"
#include "grit/generated_resources.h"

namespace about_flags {

// Macros to simplify specifying the type.
#define SINGLE_VALUE_TYPE(command_line) Experiment::SINGLE_VALUE, \
    command_line, NULL, 0
#define MULTI_VALUE_TYPE(choices) Experiment::MULTI_VALUE, "", choices, \
    arraysize(choices)

namespace {

const unsigned kOsAll = kOsMac | kOsWin | kOsLinux | kOsCrOS;

// Names for former Chrome OS Labs experiments, shared with prefs migration
// code.
const char kMediaPlayerExperimentName[] = "media-player";
const char kAdvancedFileSystemExperimentName[] = "advanced-file-system";
const char kVerticalTabsExperimentName[] = "vertical-tabs";

// If adding a new choice, add it to the end of the list.
const Experiment::Choice kInstantChoices[] = {
  { IDS_FLAGS_INSTANT_TYPE_VERBATIM, switches::kEnableVerbatimInstant },
  { IDS_FLAGS_INSTANT_TYPE_PREDICTIVE, switches::kEnablePredictiveInstant },
  { IDS_FLAGS_INSTANT_TYPE_PREDICTIVE_NO_AUTO_COMPLETE,
    switches::kEnablePredictiveNoAutoCompleteInstant
  },
};

// RECORDING USER METRICS FOR FLAGS:
// -----------------------------------------------------------------------------
// The first line of the experiment is the internal name. If you'd like to
// gather statistics about the usage of your flag, you should append a marker
// comment to the end of the feature name, like so:
//   "my-special-feature",  // FLAGS:RECORD_UMA
//
// After doing that, run //chrome/tools/extract_actions.py (see instructions at
// the top of that file for details) to update the chromeactions.txt file, which
// will enable UMA to record your feature flag.
//
// After your feature has shipped under a flag, you can locate the metrics
// under the action name AboutFlags_internal-action-name. Actions are recorded
// once per startup, so you should divide this number by AboutFlags_StartupTick
// to get a sense of usage. Note that this will not be the same as number of
// users with a given feature enabled because users can quit and relaunch
// the application multiple times over a given time interval.
// TODO(rsesek): See if there's a way to count per-user, rather than
// per-startup.

// To add a new experiment add to the end of kExperiments. There are two
// distinct types of experiments:
// . SINGLE_VALUE: experiment is either on or off. Use the SINGLE_VALUE_TYPE
//   macro for this type supplying the command line to the macro.
// . MULTI_VALUE: if enabled the command line of the selected choice is enabled.
//   To specify this type of experiment use the macro MULTI_VALUE_TYPE supplying
//   it the array of choices.
// See the documentation of Experiment for details on the fields.
//
// When adding a new choice, add it to the end of the list.
const Experiment kExperiments[] = {
  {
    "expose-for-tabs",  // FLAGS:RECORD_UMA
    IDS_FLAGS_TABPOSE_NAME,
    IDS_FLAGS_TABPOSE_DESCRIPTION,
    kOsMac,
#if defined(OS_MACOSX)
    // The switch exists only on OS X.
    SINGLE_VALUE_TYPE(switches::kEnableExposeForTabs)
#else
    SINGLE_VALUE_TYPE("")
#endif
  },
  {
    kMediaPlayerExperimentName,
    IDS_FLAGS_MEDIA_PLAYER_NAME,
    IDS_FLAGS_MEDIA_PLAYER_DESCRIPTION,
    kOsCrOS,
#if defined(OS_CHROMEOS)
    // The switch exists only on Chrome OS.
    SINGLE_VALUE_TYPE(switches::kEnableMediaPlayer)
#else
    SINGLE_VALUE_TYPE("")
#endif
  },
  {
    kAdvancedFileSystemExperimentName,
    IDS_FLAGS_ADVANCED_FS_NAME,
    IDS_FLAGS_ADVANCED_FS_DESCRIPTION,
    kOsCrOS,
#if defined(OS_CHROMEOS)
    // The switch exists only on Chrome OS.
    SINGLE_VALUE_TYPE(switches::kEnableAdvancedFileSystem)
#else
    SINGLE_VALUE_TYPE("")
#endif
  },
  {
    "vertical-tabs",  // FLAGS:RECORD_UMA
    IDS_FLAGS_SIDE_TABS_NAME,
    IDS_FLAGS_SIDE_TABS_DESCRIPTION,
    kOsWin | kOsCrOS,
    SINGLE_VALUE_TYPE(switches::kEnableVerticalTabs)
  },
  {
    "tabbed-options",  // FLAGS:RECORD_UMA
    IDS_FLAGS_TABBED_OPTIONS_NAME,
    IDS_FLAGS_TABBED_OPTIONS_DESCRIPTION,
    kOsWin | kOsLinux | kOsMac,  // Enabled by default on CrOS.
    SINGLE_VALUE_TYPE(switches::kEnableTabbedOptions)
  },
  {
    "remoting",  // FLAGS:RECORD_UMA
    IDS_FLAGS_REMOTING_NAME,
#if defined(OS_WIN)
    // Windows only supports host functionality at the moment.
    IDS_FLAGS_REMOTING_HOST_DESCRIPTION,
#elif defined(OS_LINUX)  // Also true for CrOS.
    // Linux only supports client functionality at the moment.
    IDS_FLAGS_REMOTING_CLIENT_DESCRIPTION,
#else
    // On other platforms, this lab isn't available at all.
    0,
#endif
    kOsWin | kOsLinux | kOsCrOS,
    SINGLE_VALUE_TYPE(switches::kEnableRemoting)
  },
  {
    "disable-outdated-plugins",  // FLAGS:RECORD_UMA
    IDS_FLAGS_DISABLE_OUTDATED_PLUGINS_NAME,
    IDS_FLAGS_DISABLE_OUTDATED_PLUGINS_DESCRIPTION,
    kOsAll,
    SINGLE_VALUE_TYPE(switches::kDisableOutdatedPlugins)
  },
  {
    "xss-auditor",  // FLAGS:RECORD_UMA
    IDS_FLAGS_XSS_AUDITOR_NAME,
    IDS_FLAGS_XSS_AUDITOR_DESCRIPTION,
    kOsAll,
    SINGLE_VALUE_TYPE(switches::kEnableXSSAuditor)
  },
  {
    "background-webapps",  // FLAGS:RECORD_UMA
    IDS_FLAGS_BACKGROUND_WEBAPPS_NAME,
    IDS_FLAGS_BACKGROUND_WEBAPPS_DESCRIPTION,
    kOsMac | kOsLinux | kOsCrOS,  // Enabled by default on windows
    SINGLE_VALUE_TYPE(switches::kEnableBackgroundMode)
  },
  {
    "conflicting-modules-check",  // FLAGS:RECORD_UMA
    IDS_FLAGS_CONFLICTS_CHECK_NAME,
    IDS_FLAGS_CONFLICTS_CHECK_DESCRIPTION,
    kOsWin,
    SINGLE_VALUE_TYPE(switches::kConflictingModulesCheck)
  },
  {
    "cloud-print-proxy",  // FLAGS:RECORD_UMA
    IDS_FLAGS_CLOUD_PRINT_PROXY_NAME,
    IDS_FLAGS_CLOUD_PRINT_PROXY_DESCRIPTION,
#if defined(GOOGLE_CHROME_BUILD)
    // For a Chrome build, we know we have a PDF plug-in, and so we'll
    // enable by platform as we get things working.
    0,
#else
    // Otherwise, where we know it could be working if a viable PDF
    // plug-in could be supplied, we'll keep the lab enabled.
    kOsWin,
#endif
    SINGLE_VALUE_TYPE(switches::kEnableCloudPrintProxy)
  },
  {
    "crxless-web-apps",
    IDS_FLAGS_CRXLESS_WEB_APPS_NAME,
    IDS_FLAGS_CRXLESS_WEB_APPS_DESCRIPTION,
    kOsAll,
    SINGLE_VALUE_TYPE(switches::kEnableCrxlessWebApps)
  },
  {
    "match-preview",  // FLAGS:RECORD_UMA
    IDS_FLAGS_PREDICTIVE_INSTANT_NAME,
    IDS_FLAGS_PREDICTIVE_INSTANT_DESCRIPTION,
    kOsMac,
    SINGLE_VALUE_TYPE(switches::kEnablePredictiveInstant)
  },
  // FIXME(scheib): Add Flags entry for accelerated Compositing,
  // or pull it and the strings in generated_resources.grd by Dec 2010
  // {
  //   "gpu-compositing",
  //   IDS_FLAGS_ACCELERATED_COMPOSITING_NAME,
  //   IDS_FLAGS_ACCELERATED_COMPOSITING_DESCRIPTION,
  //   kOsAll,
  //   SINGLE_VALUE_TYPE(switches::kDisableAcceleratedCompositing)
  // },
  {
    "gpu-canvas-2d",  // FLAGS:RECORD_UMA
    IDS_FLAGS_ACCELERATED_CANVAS_2D_NAME,
    IDS_FLAGS_ACCELERATED_CANVAS_2D_DESCRIPTION,
    kOsWin | kOsLinux | kOsCrOS,
    SINGLE_VALUE_TYPE(switches::kEnableAccelerated2dCanvas)
  },
  // FIXME(scheib): Add Flags entry for WebGL,
  // or pull it and the strings in generated_resources.grd by Dec 2010
  // {
  //   "webgl",
  //   IDS_FLAGS_WEBGL_NAME,
  //   IDS_FLAGS_WEBGL_DESCRIPTION,
  //   kOsAll,
  //   SINGLE_VALUE_TYPE(switches::kDisableExperimentalWebGL)
  // }
  {
    "print-preview",  // FLAGS:RECORD_UMA
    IDS_FLAGS_PRINT_PREVIEW_NAME,
    IDS_FLAGS_PRINT_PREVIEW_DESCRIPTION,
    kOsAll,
    SINGLE_VALUE_TYPE(switches::kEnablePrintPreview)
  },
  {
    "enable-nacl",  // FLAGS:RECORD_UMA
    IDS_FLAGS_ENABLE_NACL_NAME,
    IDS_FLAGS_ENABLE_NACL_DESCRIPTION,
    kOsAll,
    SINGLE_VALUE_TYPE(switches::kEnableNaCl)
  },
  {
    "dns-server",  // FLAGS:RECORD_UMA
    IDS_FLAGS_DNS_SERVER_NAME,
    IDS_FLAGS_DNS_SERVER_DESCRIPTION,
    kOsLinux,
    SINGLE_VALUE_TYPE(switches::kDnsServer)
  },
  {
    "page-prerender",  // FLAGS:RECORD_UMA
    IDS_FLAGS_PAGE_PRERENDER_NAME,
    IDS_FLAGS_PAGE_PRERENDER_DESCRIPTION,
    kOsAll,
    SINGLE_VALUE_TYPE(switches::kEnablePagePrerender)
  },
  {
    "confirm-to-quit",  // FLAGS:RECORD_UMA
    IDS_FLAGS_CONFIRM_TO_QUIT_NAME,
    IDS_FLAGS_CONFIRM_TO_QUIT_DESCRIPTION,
    kOsMac,
    SINGLE_VALUE_TYPE(switches::kEnableConfirmToQuit)
  },
  {
    "extension-apis",  // FLAGS:RECORD_UMA
    IDS_FLAGS_EXPERIMENTAL_EXTENSION_APIS_NAME,
    IDS_FLAGS_EXPERIMENTAL_EXTENSION_APIS_DESCRIPTION,
    kOsAll,
    SINGLE_VALUE_TYPE(switches::kEnableExperimentalExtensionApis)
  },
  {
    "click-to-play",  // FLAGS:RECORD_UMA
    IDS_FLAGS_CLICK_TO_PLAY_NAME,
    IDS_FLAGS_CLICK_TO_PLAY_DESCRIPTION,
    kOsAll,
    SINGLE_VALUE_TYPE(switches::kEnableClickToPlay)
  },
  {
    "disable-hyperlink-auditing",
    IDS_FLAGS_DISABLE_HYPERLINK_AUDITING_NAME,
    IDS_FLAGS_DISABLE_HYPERLINK_AUDITING_DESCRIPTION,
    kOsAll,
    SINGLE_VALUE_TYPE(switches::kNoPings)
  },
  {
    "experimental-location-features",  // FLAGS:RECORD_UMA
    IDS_FLAGS_EXPERIMENTAL_LOCATION_FEATURES_NAME,
    IDS_FLAGS_EXPERIMENTAL_LOCATION_FEATURES_DESCRIPTION,
    kOsMac | kOsWin | kOsLinux,  // Currently does nothing on CrOS.
    SINGLE_VALUE_TYPE(switches::kExperimentalLocationFeatures)
  },
  {
    "instant-type",  // FLAGS:RECORD_UMA
    IDS_FLAGS_INSTANT_TYPE_NAME,
    IDS_FLAGS_INSTANT_TYPE_DESCRIPTION,
    kOsWin,
    MULTI_VALUE_TYPE(kInstantChoices)
  },
};

const Experiment* experiments = kExperiments;
size_t num_experiments = arraysize(kExperiments);

// Stores and encapsulates the little state that about:flags has.
class FlagsState {
 public:
  FlagsState() : needs_restart_(false) {}
  void ConvertFlagsToSwitches(PrefService* prefs, CommandLine* command_line);
  bool IsRestartNeededToCommitChanges();
  void SetExperimentEnabled(
      PrefService* prefs, const std::string& internal_name, bool enable);
  void RemoveFlagsSwitches(
      std::map<std::string, CommandLine::StringType>* switch_list);
  void reset();

  // Returns the singleton instance of this class
  static FlagsState* instance() {
    return Singleton<FlagsState>::get();
  }

 private:
  bool needs_restart_;
  std::set<std::string> flags_switches_;

  DISALLOW_COPY_AND_ASSIGN(FlagsState);
};

#if defined(OS_CHROMEOS)
// Migrates Chrome OS Labs settings to experiments adding flags to enabled
// experiment list if the corresponding pref is on.
void MigrateChromeOSLabsPrefs(PrefService* prefs,
                              std::set<std::string>* result) {
  DCHECK(prefs);
  DCHECK(result);
  if (prefs->GetBoolean(prefs::kLabsMediaplayerEnabled))
    result->insert(kMediaPlayerExperimentName);
  if (prefs->GetBoolean(prefs::kLabsAdvancedFilesystemEnabled))
    result->insert(kAdvancedFileSystemExperimentName);
  if (prefs->GetBoolean(prefs::kUseVerticalTabs))
    result->insert(kVerticalTabsExperimentName);
  prefs->SetBoolean(prefs::kLabsMediaplayerEnabled, false);
  prefs->SetBoolean(prefs::kLabsAdvancedFilesystemEnabled, false);
  prefs->SetBoolean(prefs::kUseVerticalTabs, false);
}
#endif

// Extracts the list of enabled lab experiments from preferences and stores them
// in a set.
void GetEnabledFlags(const PrefService* prefs, std::set<std::string>* result) {
  const ListValue* enabled_experiments = prefs->GetList(
      prefs::kEnabledLabsExperiments);
  if (!enabled_experiments)
    return;

  for (ListValue::const_iterator it = enabled_experiments->begin();
       it != enabled_experiments->end();
       ++it) {
    std::string experiment_name;
    if (!(*it)->GetAsString(&experiment_name)) {
      LOG(WARNING) << "Invalid entry in " << prefs::kEnabledLabsExperiments;
      continue;
    }
    result->insert(experiment_name);
  }
}

// Takes a set of enabled lab experiments
void SetEnabledFlags(
    PrefService* prefs, const std::set<std::string>& enabled_experiments) {
  ListValue* experiments_list = prefs->GetMutableList(
      prefs::kEnabledLabsExperiments);
  if (!experiments_list)
    return;

  experiments_list->Clear();
  for (std::set<std::string>::const_iterator it = enabled_experiments.begin();
       it != enabled_experiments.end();
       ++it) {
    experiments_list->Append(new StringValue(*it));
  }
}

// Returns the name used in prefs for the choice at the specified index.
std::string NameForChoice(const Experiment& e, int index) {
  DCHECK(e.type == Experiment::MULTI_VALUE);
  DCHECK(index < e.num_choices);
  return std::string(e.internal_name) + about_flags::testing::kMultiSeparator +
      base::IntToString(index);
}

// Adds the internal names for the specified experiment to |names|.
void AddInternalName(const Experiment& e, std::set<std::string>* names) {
  if (e.type == Experiment::SINGLE_VALUE) {
    names->insert(e.internal_name);
  } else {
    DCHECK(e.type == Experiment::MULTI_VALUE);
    for (int i = 0; i < e.num_choices; ++i)
      names->insert(NameForChoice(e, i));
  }
}

// Removes all experiments from prefs::kEnabledLabsExperiments that are
// unknown, to prevent this list to become very long as experiments are added
// and removed.
void SanitizeList(PrefService* prefs) {
  std::set<std::string> known_experiments;
  for (size_t i = 0; i < num_experiments; ++i)
    AddInternalName(experiments[i], &known_experiments);

  std::set<std::string> enabled_experiments;
  GetEnabledFlags(prefs, &enabled_experiments);

  std::set<std::string> new_enabled_experiments;
  std::set_intersection(
      known_experiments.begin(), known_experiments.end(),
      enabled_experiments.begin(), enabled_experiments.end(),
      std::inserter(new_enabled_experiments, new_enabled_experiments.begin()));

  SetEnabledFlags(prefs, new_enabled_experiments);
}

void GetSanitizedEnabledFlags(
    PrefService* prefs, std::set<std::string>* result) {
  SanitizeList(prefs);
  GetEnabledFlags(prefs, result);
}

// Variant of GetSanitizedEnabledFlags that also removes any flags that aren't
// enabled on the current platform.
void GetSanitizedEnabledFlagsForCurrentPlatform(
    PrefService* prefs, std::set<std::string>* result) {
  GetSanitizedEnabledFlags(prefs, result);

  // Filter out any experiments that aren't enabled on the current platform.  We
  // don't remove these from prefs else syncing to a platform with a different
  // set of experiments would be lossy.
  std::set<std::string> platform_experiments;
  int current_platform = GetCurrentPlatform();
  for (size_t i = 0; i < num_experiments; ++i) {
    if (experiments[i].supported_platforms & current_platform)
      AddInternalName(experiments[i], &platform_experiments);
  }

  std::set<std::string> new_enabled_experiments;
  std::set_intersection(
      platform_experiments.begin(), platform_experiments.end(),
      result->begin(), result->end(),
      std::inserter(new_enabled_experiments, new_enabled_experiments.begin()));

  result->swap(new_enabled_experiments);
}

// Returns the Value representing the choice data in the specified experiment.
// If one of the choices is enabled |is_one_selected| is set to true.
Value* CreateChoiceData(const Experiment& experiment,
                        const std::set<std::string>& enabled_experiments,
                        bool* is_one_selected) {
  DCHECK(experiment.type == Experiment::MULTI_VALUE);
  ListValue* result = new ListValue;
  for (int i = 0; i < experiment.num_choices; ++i) {
    const Experiment::Choice& choice = experiment.choices[i];
    DictionaryValue* value = new DictionaryValue;
    std::string name = NameForChoice(experiment, i);
    value->SetString("description",
                     l10n_util::GetStringUTF16(choice.description_id));
    value->SetString("internal_name", name);
    bool is_selected = enabled_experiments.count(name) > 0;
    if (is_selected)
      *is_one_selected = true;
    value->SetBoolean("selected", is_selected);
    result->Append(value);
  }
  return result;
}

}  // namespace

void ConvertFlagsToSwitches(PrefService* prefs, CommandLine* command_line) {
  FlagsState::instance()->ConvertFlagsToSwitches(prefs, command_line);
}

ListValue* GetFlagsExperimentsData(PrefService* prefs) {
  std::set<std::string> enabled_experiments;
  GetSanitizedEnabledFlags(prefs, &enabled_experiments);

  int current_platform = GetCurrentPlatform();

  ListValue* experiments_data = new ListValue();
  for (size_t i = 0; i < num_experiments; ++i) {
    const Experiment& experiment = experiments[i];
    if (!(experiment.supported_platforms & current_platform))
      continue;

    DictionaryValue* data = new DictionaryValue();
    data->SetString("internal_name", experiment.internal_name);
    data->SetString("name",
                    l10n_util::GetStringUTF16(experiment.visible_name_id));
    data->SetString("description",
                    l10n_util::GetStringUTF16(
                        experiment.visible_description_id));

    bool enabled = enabled_experiments.count(experiment.internal_name) > 0;

    if (experiment.type == Experiment::MULTI_VALUE) {
      data->Set("choices", CreateChoiceData(experiment, enabled_experiments,
                                            &enabled));
    }

    data->SetBoolean("enabled", enabled);
    experiments_data->Append(data);
  }
  return experiments_data;
}

bool IsRestartNeededToCommitChanges() {
  return FlagsState::instance()->IsRestartNeededToCommitChanges();
}

void SetExperimentEnabled(
    PrefService* prefs, const std::string& internal_name, bool enable) {
  FlagsState::instance()->SetExperimentEnabled(prefs, internal_name, enable);
}

void RemoveFlagsSwitches(
    std::map<std::string, CommandLine::StringType>* switch_list) {
  FlagsState::instance()->RemoveFlagsSwitches(switch_list);
}

int GetCurrentPlatform() {
#if defined(OS_MACOSX)
  return kOsMac;
#elif defined(OS_WIN)
  return kOsWin;
#elif defined(OS_CHROMEOS)  // Needs to be before the OS_LINUX check.
  return kOsCrOS;
#elif defined(OS_LINUX)
  return kOsLinux;
#else
#error Unknown platform
#endif
}

void RecordUMAStatistics(const PrefService* prefs) {
  std::set<std::string> flags;
  GetEnabledFlags(prefs, &flags);
  for (std::set<std::string>::iterator it = flags.begin(); it != flags.end();
       ++it) {
    std::string action("AboutFlags_");
    action += *it;
    UserMetrics::RecordComputedAction(action);
  }
  // Since flag metrics are recorded every startup, add a tick so that the
  // stats can be made meaningful.
  if (flags.size())
    UserMetrics::RecordAction(UserMetricsAction("AboutFlags_StartupTick"));
}

//////////////////////////////////////////////////////////////////////////////
// FlagsState implementation.

namespace {

void FlagsState::ConvertFlagsToSwitches(
    PrefService* prefs, CommandLine* command_line) {
  if (command_line->HasSwitch(switches::kNoExperiments))
    return;

  std::set<std::string> enabled_experiments;

#if defined(OS_CHROMEOS)
  // Some experiments were implemented via prefs on Chrome OS and we want to
  // seamlessly migrate these prefs to about:flags for updated users.
  MigrateChromeOSLabsPrefs(prefs, &enabled_experiments);
#endif

  GetSanitizedEnabledFlagsForCurrentPlatform(prefs, &enabled_experiments);

  typedef std::map<std::string, std::string> NameToSwitchMap;
  NameToSwitchMap name_to_switch_map;
  for (size_t i = 0; i < num_experiments; ++i) {
    const Experiment& e = experiments[i];
    if (e.type == Experiment::SINGLE_VALUE) {
      name_to_switch_map[e.internal_name] = e.command_line;
    } else {
      for (int j = 0; j < e.num_choices; ++j)
        name_to_switch_map[NameForChoice(e, j)] = e.choices[j].command_line;
    }
  }

  command_line->AppendSwitch(switches::kFlagSwitchesBegin);
  flags_switches_.insert(switches::kFlagSwitchesBegin);
  for (std::set<std::string>::iterator it = enabled_experiments.begin();
       it != enabled_experiments.end();
       ++it) {
    const std::string& experiment_name = *it;
    NameToSwitchMap::const_iterator name_to_switch_it =
        name_to_switch_map.find(experiment_name);
    if (name_to_switch_it == name_to_switch_map.end()) {
      NOTREACHED();
      continue;
    }

    command_line->AppendSwitch(name_to_switch_it->second);
    flags_switches_.insert(name_to_switch_it->second);
  }
  command_line->AppendSwitch(switches::kFlagSwitchesEnd);
  flags_switches_.insert(switches::kFlagSwitchesEnd);
}

bool FlagsState::IsRestartNeededToCommitChanges() {
  return needs_restart_;
}

void FlagsState::SetExperimentEnabled(
    PrefService* prefs, const std::string& internal_name, bool enable) {
  needs_restart_ = true;

  size_t at_index = internal_name.find(about_flags::testing::kMultiSeparator);
  if (at_index != std::string::npos) {
    DCHECK(enable);
    // We're being asked to enable a multi-choice experiment. Disable the
    // currently selected choice.
    DCHECK_NE(at_index, 0u);
    SetExperimentEnabled(prefs, internal_name.substr(0, at_index), false);

    // And enable the new choice.
    std::set<std::string> enabled_experiments;
    GetSanitizedEnabledFlags(prefs, &enabled_experiments);
    enabled_experiments.insert(internal_name);
    SetEnabledFlags(prefs, enabled_experiments);
    return;
  }

  std::set<std::string> enabled_experiments;
  GetSanitizedEnabledFlags(prefs, &enabled_experiments);

  const Experiment* e = NULL;
  for (size_t i = 0; i < num_experiments; ++i) {
    if (experiments[i].internal_name == internal_name) {
      e = experiments + i;
      break;
    }
  }
  DCHECK(e);

  if (e->type == Experiment::SINGLE_VALUE) {
    if (enable)
      enabled_experiments.insert(internal_name);
    else
      enabled_experiments.erase(internal_name);
  } else {
    if (enable) {
      // Enable the first choice.
      enabled_experiments.insert(NameForChoice(*e, 0));
    } else {
      // Find the currently enabled choice and disable it.
      for (int i = 0; i < e->num_choices; ++i) {
        std::string choice_name = NameForChoice(*e, i);
        if (enabled_experiments.find(choice_name) !=
            enabled_experiments.end()) {
          enabled_experiments.erase(choice_name);
          // Continue on just in case there's a bug and more than one
          // experiment for this choice was enabled.
        }
      }
    }
  }

  SetEnabledFlags(prefs, enabled_experiments);
}

void FlagsState::RemoveFlagsSwitches(
    std::map<std::string, CommandLine::StringType>* switch_list) {
  for (std::set<std::string>::const_iterator it = flags_switches_.begin();
       it != flags_switches_.end();
       ++it) {
    switch_list->erase(*it);
  }
}

void FlagsState::reset() {
  needs_restart_ = false;
  flags_switches_.clear();
}

} // namespace

namespace testing {

// WARNING: '@' is also used in the html file. If you update this constant you
// also need to update the html file.
const char kMultiSeparator[] = "@";

void ClearState() {
  FlagsState::instance()->reset();
}

void SetExperiments(const Experiment* e, size_t count) {
  if (!e) {
    experiments = kExperiments;
    num_experiments = arraysize(kExperiments);
  } else {
    experiments = e;
    num_experiments = count;
  }
}

const Experiment* GetExperiments(size_t* count) {
  *count = num_experiments;
  return experiments;
}

}  // namespace testing

}  // namespace about_flags