text: // Copyright 2014 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 BASE_METRICS_USER_METRICS_H_
  #define BASE_METRICS_USER_METRICS_H_
  
  #include <string>
  
  #include "base/base_export.h"
  #include "base/callback.h"
  #include "base/metrics/user_metrics_action.h"
  #include "base/single_thread_task_runner.h"
  
  namespace base {
  
  // This module provides some helper functions for logging actions tracked by
  // the user metrics system.
  
  // For best practices on deciding when to emit a user action, see
  // https://chromium.googlesource.com/chromium/src.git/+/HEAD/tools/metrics/actions/README.md
  
  // Record that the user performed an action.
  // This function must be called after the task runner has been set with
  // SetRecordActionTaskRunner().
  //
  // "Action" here means a user-generated event:
  //   good: "Reload", "CloseTab", and "IMEInvoked"
  //   not good: "SSLDialogShown", "PageLoaded", "DiskFull"
  // We use this to gather anonymized information about how users are
  // interacting with the browser.
  // WARNING: In calls to this function, UserMetricsAction should be followed by a
  // string literal parameter and not a variable e.g.
  //   RecordAction(UserMetricsAction("my action name"));
  // This ensures that our processing scripts can associate this action's hash
  // with its metric name. Therefore, it will be possible to retrieve the metric
  // name from the hash later on.
  //
  // Once a new recorded action is added, run
  //   tools/metrics/actions/extract_actions.py
  // to add the metric to actions.xml, then update the <owner>s and <description>
  // sections. Make sure to include the actions.xml file when you upload your code
  // for review!
  //
  // For more complicated situations (like when there are many different
  // possible actions), see RecordComputedAction().
  BASE_EXPORT void RecordAction(const UserMetricsAction& action);
  
  // This function has identical input and behavior to RecordAction(), but is
  // not automatically found by the action-processing scripts.  It can be used
  // when it's a pain to enumerate all possible actions, but if you use this
  // you need to also update the rules for extracting known actions in
  // tools/metrics/actions/extract_actions.py.
  // This function must be called after the task runner has been set with
  // SetRecordActionTaskRunner().
  BASE_EXPORT void RecordComputedAction(const std::string& action);
  
  // Called with the action string.
  using ActionCallback = RepeatingCallback<void(const std::string&)>;
  
  // Add/remove action callbacks (see above).
  // These functions must be called after the task runner has been set with
  // SetRecordActionTaskRunner().
  BASE_EXPORT void AddActionCallback(const ActionCallback& callback);
  BASE_EXPORT void RemoveActionCallback(const ActionCallback& callback);
  
  // Set the task runner on which to record actions.
  BASE_EXPORT void SetRecordActionTaskRunner(
      scoped_refptr<SingleThreadTaskRunner> task_runner);
  
  }  // namespace base
  
  #endif  // BASE_METRICS_USER_METRICS_H_
  